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Disabling ESC, torque vectoring, curve control & changes to handling characteristics

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Disabling ESC, torque vectoring, curve control & changes to handling characteristics

As the title states I've been curious what the ST would behave like with some of the electronic driving and chassis aids disabled. Due to how a lot of stability control, the torque vectoring and curve control features are implemented using the ABS (anti-lock brake system) controller I doubt there will be any way in the short-term to disabled them via current tuning solutions that interface with the Bosch powertrain controller.

So how can they be disabled and what do the different modes and features do? The "sport" mode on the ESC (electronic stability control) raises thresholds where stability control will intervene but apparently doesn't alter the torque vectoring and doesn't seem to change the curve control characteristics if you dive into a corner a little too hot. If you use the full ESC "off" mode it turns off the stability control, which can help rotate the car by braking individual wheels when grip is exceeded, but the torque vectoring and likely curve control are still active. My temporary solution to test how the car behaves without these electronic features was to disable the ABS as all of them utilize the brakes or a combination of braking and power modulation to bring about desired wheel rotational characteristics (i.e. slow individual or multiple wheels in order to rotate the car and/or transfer power to the other wheel in the case of the front wheels while accelerating).

To go off on a tangent for a moment so everyone understands what the electronic systems are doing, torque vectoring can be thought of and is often referred to as an electronic limited slip differential, also sometimes referred to as a brake-lock or brake-limited (limiting) differential. The six-speed Ford MMT-6 transaxle used in the ST has an open differential (diff) which means when traction is lost due to poor road surface conditions or when exceeding available traction at one or more front wheels the diff will still attempt to send torque to the wheel that has lost traction and because it can't send more torque to the wheel that hasn't slipped than what it can send to the spinning wheel it results in a loss of forward acceleration. A conventional limited slip or automatic torque biasing diff uses internal clutch packs or gears inside the differential to ensure engine torque is also transferred to the wheel with traction instead of an open diff having one wheel spinning and little to no torque going to the other wheel.

The torque vectoring or electronic, brake-based "diffs" work by acting on a spinning wheel at the rotor and slowing it to ensure torque is transferred through the open differential to the wheel with traction. This generally isn't as seamless in operation, isn't as quick to respond since the computer has to sense an impending spin condition then apply the brakes in order to transfer power, and because of how it uses the brakes it does utilize some of the brake capacity to scrub off wheel speed which increases rotor and pad temps. For daily driving and an occasional spirited drive or for short track events they can work pretty good but usually aren't preferred for heavy track use.

Electronic stability control (ESC) works by using yaw (rotational) and lateral accelerometer sensors in addition to a steering angle sensor to determine if the vehicle goes over a preset limit where the controller determines the car is sliding and/or watches the desired steering wheel angle and can tell when the car is understeering or oversteering and not going in the intended direction of travel. It then engages brakes at individual wheels at each corner to help rotate the car into the intended path of travel or correct oscillations that might cause the vehicle to spin. There are three modes on the ST, full on which does allow for a little vehicle slip before it intervenes, a sport mode that allows you to track the car but still have the system step in if you exceed the chassis and tire limits if the car is about to spin and full off mode that completely disables this safety net.

The Curve Control feature was a little more difficult to figure out what exactly it's doing on a technical and system level. The intent is that if you enter a corner or curve too fast, such as a highway off-ramp, the system will intervene to help maintain the desired path of travel. Ford also advertises an electronic understeer control feature but this appears to be primarily provided as part of the torque vectoring if the car is accelerating. During braking or when the controller detects there is impending deceleration coming into a corner the Curve Control or stability control functionality appears to be responsible for actively reducing understeer (front end "push" or the tendency to continue in the direction of travel vice turning into the corner).

Curve Control does this by using the stability control system (which again is likely based primarily in the ABS controller programming) to determine you're possibly about to enter a corner or curve by looking at sensor readings such as the steering wheel angle and other sensors and how readings start to ramp up as the vehicle begins into the turn. The moment you start to brake or request more steering angle than you'll have traction available it immediately applies full braking force before the car has started to rotate into the turn (curve control), then applies individual braking at each corner (ESC, and as necessary) as a preemptive stability control feature to help reduce understeer before the need for full stability control to intervene and correct for a maneuver that has already exceeded the vehicle's dynamic limits. Ford quotes the system as being able to scrub off ~10 mph as soon as you first apply the brake pedal.

All these features are made possible by sensor data and computer algorithms to determine desired chassis and handling characteristics. The controllers then utilize engine torque management and ABS to modulate individual wheel speed to change directional behavior characteristics of the vehicle. Basic traction control for example uses the ABS wheel speed sensors to determine when one or both wheels are spinning (compared to each other and/or the rear, non-driven wheels on a front wheel drive vehicle) and can reduce engine torque to bring the spin under control by closing the throttle, altering ignition timing and/or reducing boost. If that isn't effective it can also use the braking system to apply just enough brake pressure to stop the wheel over-speed (spin) condition.

The anti-lock braking behind most of these features uses highly accurate wheel speed sensors and an integral hydraulic control unit (HCU) that contains a hydraulic pump to build brake pressure without having the driver press on the brake pedal, a controller module that provides the logic to drive the systems, and a valve body assembly that has a valve for controlling brakes pressure to each wheel (with that pressure provided by the hydraulic pump and/or driver brake force from the brake master cylinder). The valves work by opening to allow brake fluid to pass, increasing braking force or closing and allowing fluid to return to the master cylinder/ABS HCU and therefore reduce pressure to a specific wheel. Older ABS used to have a fixed duty-cycle that could only switch these valves on and off a set number of times per second but some newer systems use pulse width modulation (PWM) on the valve solenoids to be able to continually vary braking pressure to each wheel. This is why you don't feel the ABS buzzing in the brake pedal when these stability or torque vectoring features are active on the ST.

A few other features made possible by ABS are panic brake assist, electronic brake force distribution (EBFD, often called EBD) and hill start assist. Panic brake assist uses algorithms that watch how quickly you let off and close the throttle (i.e. how fast you get off the gas) and then how quickly you get on the brake pedal. If the system determines you're possibly attempting a panic or emergency stop that requires full brake force it will automatically use the ABS hydraulic pump to apply full brake pressure up to the anti-lock modulation threshold before you've had time to fully depress the brake pedal. This can have a significant impact on the time required to fully engage the brakes and bring the vehicle to a stop. It doesn't seem quite as noticeable on the ST compared to implementations in some earlier vehicles but if you do experience it you can easily disable or cancel it by slightly letting off on the brake pedal. These systems normally assume you aren't left foot braking which may cause premature application of the feature under certain circumstances.

Electronic brake force distribution (EBD) uses the ABS system in place of (or occasionally to supplement) a conventional rear-brake proportioning valve. On older cars prior to the advent of modern ABS they would use a mechanical proportioning valve inside the hydraulic braking circuits between the front and rear brakes to ensure the rear wheels didn't receive too much pressure in a stop that would cause them to lock up. The brake master cylinders normally provide a variable amount of fluid between the front and rear circuits depending on how hard and fast you get on the brake pedal, but under most stops the rear brakes only provide a small portion of the total braking force (often in the 15-25% range). In a panic stop when the nose of the car is diving due to weight transfer, if you were mid-corner and the rear brakes received too much pressure they would lock up and it would be easy to lose control.

The brake master cylinder provides a very rough amount of brake pressure differentiation between front and rear depending on how you apply the brake pedal but it's the proportioning valve that limits how fast and how much brake pressure can ramp up in the rear circuit/wheels. EBD takes this further and instead of a somewhat fixed response a mechanical valve provides the EBD can dynamically use the valves in the ABS HCU to limit and control changes in pressure to the rear wheels on a continually adjustable nature. This means it can adjust for things like different vehicle loads, surface conditions, changing chassis dynamics, etc.

If you're coming to stop slowly it can use more rear brakes which helps increase front pad life. In a heavier braking application it can apply the exact amount of needed rear brake force without upsetting the chassis, such as during mid-corner braking. It does this by using precision, four-channel ABS (where each wheel has it's own wheel speed sensor and control circuit) to watch the rear wheel speed and can tell when a wheel is nearing impeding lock-up under heavy braking. It also continually compares rate of deceleration changes between the front and rear wheels and under light braking can use more rear bias than a conventional proportioning valve would provide when lockup is unlikely to occur. Some EBD implementations also integrate into the stability control system but prior to the US federal mandate for ESC there were quite a few cars with ABS and EBD but no ESC (and I won't use anymore acronyms in this sentence).

Back to the question at hand, how does the ST behave with ESC, torque vectoring, and curve control disabled? Since they all use ABS it would seem simple to just kill that system. We can't disable it via software (i.e. tuning changes to the ABS controller) so that leaves us with removing the ABS fuse or disconnecting a wheel speed sensor. I chose to disconnect a front wheel speed sensor as the system won't be able to compare wheel speed differences across the front axle and therefore can't provide torque vectoring. Disconnecting a rear sensor may very well disable the entire system as well but will require further testing. In any case if any of the four wheel speed sensor aren't working it will disable stability control and anti-lock braking. If I had chosen to pull the ABS fuse this would also have disabled EBD and caused the system to default to a fixed front-to-rear bias ratio that might cause the rear wheels to lock up prematurely.

The initial thing I noticed after I disconnected the front, driver-side wheel speed sensor was an increase in steering effort. It took me a moment to realize that the speedometer was also inoperative which means Ford is using the ABS controller's front wheel speed sensor to provide the powertrain controller with vehicle speed information vice using a separate vehicle speed sensor (VSS) on the output shaft of transaxle or the drive axle. When the car can't determine vehicle speed it appears to default to a fixed power assist level that makes for slightly heavier parking lot speed steering and the assist also seems to remain linear. Normally you get more assist at parking lot and lower speeds and the assist decreases as the vehicle speed increases.

I ended up taking the car on about 15 miles of twisty two-lane backcountry roads that I'm very familiar with and drive on a weekly basis. The speed limit in this canyon and hilly area is around 45 mph in most sections and it includes some decreasing radius, hairpin and various other turns as the road rises and falls. The surface ranges from fairly smooth to areas that have rougher, broken pavement.

Without the above-mentioned stability and torque vectoring aids the character of the car changes quite a bit. It's very apparent the chassis was tuned as a complete system and it's assumed these electronic systems will be available and working when driving the car at higher speeds and approaching its limits. One of the first things I noticed when diving into a corner a little on the fast side was that the slightly unnatural, low amount of understeer was gone. In its place was what I'd expect from a sporting, nose heavy front drive car and it started to push into slight understeer much more readily. The limits are still very high and the tires provide a commendable amount of grip but the video game like nature of how the car rotates was gone.

Getting back on and off the throttle and using it to modulate power and weight transfer still provided a means to help rotate the car but isn't quite as natural and the chassis didn't feel anywhere near as balanced without the electronics. For example if you come into a corner a little quick or too low and start to understeer, if you reducing braking to transfer weight back to the front wheels, the rear end that normally feels very controllable and lively starts to feel twitchy and like it might step out. I think a lot of this is due to the super-quick steering ratio once you move off-center and are approaching the 10.1:1 range. You can still control the car but it doesn't feel as cohesive.

When you get through a corner and are getting back on the throttle the next surprise appears. If you romp on the throttle with the electronics active I've still seen a little bit of wheel spin which led me to wonder how affective the torque vectoring, braked-based limited slip function works. With it disabled it becomes pretty apparent that it does work even if not to the level of a true mechanical limited slip. Coming out of a couple corners where I applied nearly full throttle it roasted the tires and I had to significantly back off the throttle reducing forward momentum.

This significant reduction in power and the time it took me to make that change would take a lot longer and slow the vehicle much more than just letting the torque vectoring step in. I've seen some concerns that by using the brakes to control wheel speed it is slowing the vehicle and while that might technically be true the system is primarily controlling a wheel that already isn't contributing to forward motion and transferring power to the wheel that can, and does so much faster than a human could intervene by backing off the throttle in an attempt to restore traction.

As the road straightened out and I had a chance to do some acceleration from a stop in a straight line and acceleration from a stop going into slight turns and torque steer seemed about the same as it was with the electronics enabled. I've been driving the Focus for many years and even my stock SVTs have twitchiness to them when accelerating hard on undulating surfaces (i.e. mild torque steer). The European C1 cars haven't been a lot better in this regard and we've seen how this chassis has done for the Mazdaspeed 3 and most press noting how that with significant engine torque applied the wheel tugs quite a bit. The Focus and it's platform provides great handling but has always seemed a touch prone to torque steer. Whether that's due to one or a combination of suspension geometry, tire sidewall, axle design and alignment or another number of factors is unknown.

Accelerating through a corner the torque steer didn't seem an issue either but I suspect that was because the inside wheel was lit up spinning and not providing enough traction. Should there have been enough grip it may have tugged at the steering wheel more but even with ABS disabled the electronic controlling the electrical assist motor on the rack are likely still working. It's difficult to say but when someone installs a true limited slip diff we'll have a better idea how the car will behave. I'd also like to see how the car behaves with the electrical steering disabled but want to verify with TRW that the belt-driven motor system won't be damaged if driven for an extended period without power.

Overall I summarize the experience as indicative of the true nature of the chassis. There's lots of grip but it does rely heavily on the electronics working as a team with the chassis tuning to produce the best results. Without them the steering becomes twitchy as you're wondering if (when) the rear steps out too far if you'll be able to perform super precise counter-steering since any small change in steering angle moves the front wheels so much. The steering, which has receive minor criticism as feeling a touch numb doesn't feel better with increased effort. It just feels heavier with no increased feedback or road feel and you can't tell what the contact patch is doing. Without the electronics it can't effectively put down power and won't be able to pull the car out of corners without lighting up a tire.

When everything is working together it works well. Quite well. And therein lies the next question for owners who are always looking to improve their vehicles. Ford spent a lot of effort getting the ST to ride somewhat smoothly, absorb impacts and bend into a corner with haste. It does this by using some electronic wizardry that purists might not appreciate but the end results are impressive. For someone wanting to drop suspension parts onto the car they'll need to evaluate if handling is a priority or if they want the appearance changes. For those wanting to make the car turn even better or improve ride quality and maintain stock levels of handling it will require careful upgrades and likely some trial and error in hopes of improving while working with the systems Ford spent countless hours developing and refining.
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Interesting. Thanks for taking the time to post this. Your findings were fairly predictable but it's nice to have someone put in the effort to test & document.
Very well written and informative. I was wondering why I didn't feel the abs vibration with this car I did in the VW.

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A question slightly off topic is PWM what allows them to use drum brakes with ABS and ESC? I know early on in the ABS ESC days it always required disc all around. And from my experience with our Fiesta the system doesn't seem to suffer at all having drums in back and with that car being as light as it is I'm not sure it really needs disc for normal street use. If I'm in the mountains I just turn on the hill mode on the transmission and let it use the engine to keep speed in check going downhill.
Excellent post. Always like reading what you have to say Blackbird.
Great stuff. Really interesting and very informative. Personally, vorsprung durch technik. I have no problems with the electronics being an integral part of the car - all I know is that I love the way it handles, and it's both a blast to drive and a comfy daily driver. Now to bring on the I can drive it daily.
A question slightly off topic is PWM what allows them to use drum brakes with ABS and ESC? I know early on in the ABS ESC days it always required disc all around. And from my experience with our Fiesta the system doesn't seem to suffer at all having drums in back and with that car being as light as it is I'm not sure it really needs disc for normal street use. If I'm in the mountains I just turn on the hill mode on the transmission and let it use the engine to keep speed in check going downhill.
I haven’t seen anything directly noted in any tech papers on the subject but that wouldn’t surprise me. With some of the older generation integrated ABS HCUs it was possible to have a four-channel system and rear drum brakes but usually the automakers would install a simpler three-channel ABS to save money (a four-channel ABS uses four different hydraulic control circuits with individual solenoids/valves to control brake pressure to each rear wheel vice a three-channel system that has sensors at all four wheels but modulates both rear wheels together during anti-lock conditions).

Before the US federal mandate for stability control a lot of the stability control systems were an extra cost, expensive option which also normally came with rear disc brake upgrades (I’d suspect primarily for the marketing aspect) but it was possible to have a four-channel ABS with stability control and rear drum brakes. The systems weren’t pulse-width modulated (PWM) and were much cruder and noticeable when the system stepped in than the newer ABS HCUs but that applied even to ABS assisted braking and not just stability control. How many new cars rattled and shook the brake pedal like an 8.5 magnitude earthquake under ABS assisted stops just a couple decades ago?

Drum brakes are still less expensive for an automaker and they can work very well, especially with newer ABS controllers that can better modulate pressure between the front discs and rear drums on a continually variable basis. Since the great majority of a car’s stopping is done by the front brakes during a heavy braking application the drums work fine. The slight downside is pedal feel can suffer somewhat due to the difference in fluid volume required to act on a rotor brake’s caliper piston compared to the volume needed for the brake cylinder used to actuate the drums’ shoes/pads (which again can be partially mitigated by using electronic brake-force distribution (EBD) instead of a conventional mechanical proportioning valve).

Drum brakes also don’t shed heat anywhere near as well as ventilated or even solid discs. This is the biggest downfall for use in motorsport type applications as the shoes can eventually overheat and start to fall apart under extreme temps if the drum is too small. If the drum is bigger and finned to withstand higher thermal loading and abuse for longer periods of time it can significantly increases unsprung mass and the proportioning and modulation become an issue with older, conventional braking systems.
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The old school purists might not like the electronics, but I really wonder what the new school people could do if they could reprogram the system. The extent of handling wizardry that is possible with the electronics suggests further wizardry is possible for someone creative and skilled enough. Or even have different electronic tuning for different types of tracks.
As others have said, thanks for this post, and generally, for the level of care and information you put into all your posts.

I love the look of a slightly dropped car, but I'm not going to mess with the suspension. The only reason I purchased this car over a GTI was that all reviewers had unanimously concluded that Ford's suspension tuning was best in class. I don't think the build quality or interior/exterior design can match VW, but the handling of the ST (and the work that Ford engineers put into it) put the GTI to shame. The only negative is the torque steer, but that is a product of the powerful engine and is, at least to my mind, part of the fun of the car.

That said, I know that some people have installed the Steeda sway bar, and liked the results. But it would be great to get a more precise idea of how that modification would change the car's handling feel.
Thanks for the post blackbird, lots of great info. I'd like to also know how an LSD will perform. I might bite the bullet and install one, but not just yet.

I'm not sure if you're aware, but even with the AdvanceTrac ESC disabled, the curve control and eTVC remains acitve on the ST.
Yes, thought that was mentioned but that's why I disabled the ABS by disconnecting a front wheel speed sensor so it wouldn't be able to apply any of the curve control or torque vectoring but leave the electronic brake-force distribution active. If I get a chance I might try it out again by disconnecting a rear wheel sensor, as those are much easier to get to without putting the car on jack stands. That way it shouldn't disable the vehicle speed input to the computer and speedometer and cause the power steering system to default to a pre-set level of assist.
Im wondering if adding an LSD would conflict with the eTVC. Any thoughts?
....think we have that going on in the ST Performance area under Quaife LSD
Disabling ABS via various methods and effects on braking and brake bias

It's been a while since I last updated the thread but I've continued to do some testing and making observations with the electronics disabled, continuing to look at handling and chassis dynamics but focusing on torque steer and anti-lock braking. In this segment I’ll be covering braking and the methods of disabling the torque vectoring type functions which might interest those planning on taking their car to the track to see how it behaves without the torque vectoring type functions enabled.

To recap, without access to the programming in the ABS HCU (hydraulic control unit) controller I would be surprised if there is any way to fully disable the torque vectoring stability and traction control functions via current software tuning solution. The AdvanceTrac stability control does offer three modes, the “Normal” full on, “Sport” mode where the computer allows for more wheel spin and high yaw and slip angles before stability control steps in, as well as the “Off” mode. With it off you’ll find it easier to light up an inside tire under heavy acceleration mid-corner and the stability control system won’t selectively brake individual wheels to rotate the car to assist in keeping the vehicle going on the directed path of travel the system is still applying braking on the front axle for the torque vectoring, curve control type features to help put the power down and aid in rotating the vehicle. You can get the car to slip and slide all over the place and the conventional stability control functionality won’t interfere but the other features still have some impact on the chassis dynamics and stability (but aren’t acting on their own to bring the car under control). From the ST Owner’s Manual Supplement Ford describes it as follows:

Enhanced torque vectoring control (eTVC) is comprised of two elements:
• Torque vectoring control which applies brake torque on the inner
wheel in a curve for better traction and less understeer
• Cornering understeer control which controls the yaw response of the
vehicle under braking and acceleration on high and low friction
Unlike ESC, eTVC control does not slow the vehicle but does help
control excessive wheel slip and gives the vehicle cornering agility. The
system only increases performance. Because of this, eTVC is not disabled
when the AdvanceTrac system is off.

Since we can’t disable it in software (the tuning tools like the currently available SCT and Cobb solutions are only for the Bosch powertrain controller and not the ABS controller), that leaves us with three somewhat easy methods to full disable all brake-based electronic aids: 1.) disconnect a front wheel speed sensor, 2.) disconnect a rear wheel speed sensor, and 3.) pull the ABS module fuses. I differentiate between the front and rear sensors because each method produces slightly different results discussed below.

Probably the easiest method without having to crawl under the car to disconnect a wheel speed sensor is to remove the ABS fuse from the underhood power distribution box. According the manual there are three fuses that affect the ABS, fuse F19 for the controller (5A, “Anti-lock brake system/Electronic stability program 15 feed), fuse F8 likely for the solenoid pack in the HCU (30A, “Electronic stability program valve”) and fuse F7 for the pump motor used to build hydraulic brake pressure without the operator having to press the brake pedal (40A, “Anti-lock brake system/Electronic stability program pump”). All three of these fuses are located in a module and can be removed together or individually by opening the cover on the fuse carrier.

This method will completely disable the ABS HCU and all anti-lock braking and stability related functions but is generally not the preferred method for disabling stability or traction control on cars that lack a true on-off switch like the old SVT Focus (that car did have a switch to disable traction control but only killed the powertrain controller traction functions such as reducing ignition timing to decrease power to bring a spinning wheel under control but it couldn’t disable the ABS-based braking features which were still used and active below 25 mph/40 km/h even with traction control set to “off”). The reasons why pulling the ABS fuse is often frowned upon is due to most newer cars using the ABS for electronic brake force distribution (EBD) as discussed earlier in the thread. Without a mechanical proportioning valve to control brake pressure gain between the front and rear wheels and no EBD active many cars will prematurely lock the rear wheels.

I wanted to find out if this was the case so I headed out to a dirt county road where I could practice varying levels or brake application force, application time and braking from different speeds. Upon pulling the ABS fuses the first thing I noted was that the speedometer and odometer stopped working and the expected ABS and warning lights came on with one exception, the red “Brake” light was also on. This generally comes on only when there’s a problem with the mechanical braking system such as low fluid level in the reservoir due to the pressure switch reporting a fault on the master cylinder.

After driving a short distance another unexpected light also came on, the supplemental restraint or “airbag” light. This is pretty logical as the airbag controller needs to know the vehicle speed to use in combination with the deceleration sensors to calculate if you’re going fast enough and have an impact with enough force to trigger an airbag deployment (normally around 12-18 mph in most cars to prevent a deployment in low speed collisions such as in a parking lot, for example).

With the fuses out and still on asphalt pavement I performed a braking application at about 35 mph with moderate force and engagement speed and was rewarded with the left rear wheel locking up and the rear of the car stepping out hard to the side. Without immediately modulating braking pressure this likely would have required an application of counter-steer has this been on a surface with less traction. After proceeding to my dirt testing area I confirmed that with the ABS fuse pulled there is a dramatic change in rear wheel bias once the EBD function is disabled. On dirt and regular pavement it is still possible to brake with a good amount of stopping force but if the physical master cylinder ramps up pressure too quickly or if the roads are poor the rear wheels always lock up first and in a manner that is unforgiving at higher speeds and also affects lower speed braking if you lay into the pedal too much.

A couple other items of note, with the ABS fuse disabled the car has no way to obtain vehicle speed from any of the active-style, powered ABS sensors (which work like a Hall effect sensor and are more accurate than older, passive sensors). As such the powertrain controller can’t tell how fast you’re moving and it appears to slightly reduce power. Without digging through the calibration and programming/algorithms in the powertrain controller it is probably registering a default and falling back to a fail-safe or certain tables and cells aren’t active and being used with no vehicle speed input. The last minor item to note is that in the driver information screens on the instrument panel display, even with close to a half dozen warning lights lit up the System Check screen doesn’t provide any additional information, instead showing all systems as normal.

Next up was a comparison to normal, fully enabled operation. The first start after replacing the ABS fuse turned off all lights with no lingering check engine or braking system indicators. Both on pavement and the dirt road the ABS works well with smooth modulation and excellent vehicle control.

The next test was to disconnect an ABS sensor and I started with the rear wheel. As noted earlier in the thread if you disconnect a front wheel speed sensor the speedometer stops working and the electrically assisted power steering defaults to a very low, fixed level of assist. I did note this time that the odometer kept working with either a front or rear sensor disconnected. With the rear sensor unplugged the speedometer works and you have normal power steering assist. With just the ABS wheel speed sensors unplugged, either at the front or at the rear (I didn’t test with multiple sensors unplugged) the amber colored ABS malfunction indicator lamp comes on but the red “Brake” light does not compared to what happened when pulling the ABS fuse. Why this happens becomes pretty apparent after the first moderate stop on poor road conditions.

Unlike what happened when pulling the ABS fuses where there was extreme rear wheel brake bias and both tires would lock up harshly, with just the ABS wheel speed sensors disconnected it does appear the EBD function is still active. The rear brakes still have a tendency under quick and hard braking application to lock up first but it is nowhere near as bad as with the ABS disabled via the fuse. The system may not be able to modulate brake bias front to rear to account for vehicle load, weight transfer, speed and force when the brake pedal is applied among other factors but it still gives a somewhat normal brake bias.

To summarize:

1.) Remove ABS fuse block
- Disables speedometer and odometer.
- Disables anti-lock braking and all functionality relying on it.
- Disables electronic brake force distribution (EBD) biasing for the rear wheels.
- Rear wheels of car extremely likely to lock up under moderate braking.
- Disables supplemental restraint system (airbags).

2.) Disconnect front wheel ABS speed sensor
- Disables speedometer (odometer still works).
- Power steering defaults to fix, low level of assist.
- Anti-lock braking and functionality relying on it disabled but EBD still active.
- Slight tendency towards rear wheel bias under braking (likely but not always first to lock up).

3.) Disconnect rear wheel ABS speed sensor
- Anti-lock braking and functionality relying on it disabled but EBD still active.
- Slight tendency towards rear wheel bias under braking (likely but not always first to lock up).
- Speedometer, odometer and power steering operate as normal.

With the ABS fuses pulled I’d say it isn’t safe to drive the car on the street. With no brake force distribution between the front and rear brakes the rear end of the car will lock up and step out with ease. This likely explains why Ford triggers the red, mechanical service brake “Brake” light when the ABS system isn’t powered. You still have normal braking power but it is undirected with too much force going to the rear. For someone on the track, if you’re running giant, sticky, non-staggered size tires or running a much more aggressive brake pad compound up front it might be a way to get more braking force to the rear or lock up and slide the rear if that suits your style but for the majority of people they’re probably best served not to pull the fuse.

That brings us to the wheel speed sensors. If you want to explore what the ST is like without the torque vectoring and corner control features behaving the car disconnecting a front sensor will increase steering effort and give some extra weight to the steering but you lose the speedometer while disconnecting the rear sensor leaves the speedometer and steering unaffected. Without the torque vectoring the car isn’t as cohesive and tossing it around corners leads to more understeer. The tail will still want to step out like on a stock, normally operating car but you won’t have the electronics there to help control this in a progressive manner. As such, with the increased steering effort afforded by disconnecting a front sensor it seems a little easier to dial in the right amount of counter-steer.

With the rear wheel sensor disconnected and normal steering behavior the once playful variable-ratio steering rack and reduced driver effort from the power assist (with assist still quite noticeable at speed compared to with the front sensor disconnected) the steering is twitchy and doesn’t harmonize with what the chassis is doing. On public roads that appeal to enthusiast you aren’t rewarded with a sense of confidence that a stock behaving car gives and the balance front-to-rear just doesn’t seem there.

On a short auto-x or safe road course it might be something to play around with if you’re trying to figure out how the car behaves without the electronics and to help determine what suspension changes may do to the chassis. I mentioned earlier in the thread but the ST really was developed as a complete package of suspension and chassis tuning and the electronics which when working together is pretty impressive. Without them the ST feels more like a regular, nose heavy front drive sporting car, more prone to push in corners but with less balance in just the chassis than the best of the breed with a fast but numb steering that doesn’t provide a ton of feedback and filters out pavement imperfections.

One last thing that I might get around to testing is to see if the ABS pump fuse is pulled (fuse F7) if the EBD is still active. Pulling the whole carrier module of the three fuses completely kills the system including broke force distribution but I suspect pulling just the pump fuse will disable the brake-based functions but the controller and HCU solenoid pack should still receive power and be able to default to a fixed brake bias vice being unpowered and a majority of brake force going to the rear. This would make it a little easier to explore the car’s behaviors without the need to disconnect wheel speed sensors.

Speaking of which, there is a small slip near the cable/wiring side of the sensor that needs depressed in order to disconnect the sensor. If you go off feel alone the main body of the sensor will flex and feels like it has a locking tab on the side of the body but you need to press this smaller clip near the end/top (also there’s no locking tab on the sensors that needs disengaged prior to pressing the removal clip). Even disconnected they stay in place fairly well and don’t look like they will get caught up in or bind up on suspension components as the vehicle is driving. If someone wanted to leave it disconnected long-term it might be good to relocate it to reduce vibration and stress on the internal wiring and cover the open end of the connector with a weatherproof tape.
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Is it a Bosch system? I think the MKV VW Rabbit that I owned previously was using a Continental system.

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GOOD POST!!! I have had my ST for bout 9 months now and I have used normal and sport modes exclusively... no track runs yet.. but I have driven it in "track mode" and that is exactly what it should be used for... open track.. with room to get loose!!! it is basically a "normal" car in track mode... not to be pushed in rural traffic conditions.. what it should have been called was drift mode.. which is what I believe they are calling it for the RS. Now what I know about normal vs. sport mode... normal mode is basically "mid-west weather mode... It is for daily driving in the transitional months such as all of them except July and August... those 2 months sport mode is OK everyday...LOL. But seriously... Sport mode has much smoother shift engagements... especially between 1,2 and 2,3 shifts.. I'm assuming it is due to the fact that "sport" mode allows more wheel slip before engaging the ESC system. Driving in normal mode.. I'm always feeling a more jerky engagement on 1,2 and 2,3 shifts... now driving in the rain.. normal mode with ESC fully engaged... BOSS!!! Thank you Ford for giving me options for different road conditions.. now if you would have offered people in the mid-west an all-season tire option... that would have been great... cause I really hate driving my POS Pontiac Sunfire every time it snows!!!
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3.) Disconnect rear wheel ABS speed sensor
- Anti-lock braking and functionality relying on it disabled but EBD still active.
- Slight tendency towards rear wheel bias under braking (likely but not always first to lock up).
- Speedometer, odometer and power steering operate as normal.
sorry to bring this back to life.
but i've been doing a lot of track events lately and the eTVC is just over working the brakes like crazy.
i'm wondering if you've tried unplugging the rear sensor and drove it on a track.
Or any of your findings can provide information or concerns for on the track application.

Sorry about the late reply. I didn't get a chance to track the ST with the system disabled but ages ago would use a disconnected rear wheel ABS sensor on my SVT Focus to kill the non-defeatable below 25 mph traction control for the drag strip. On that car it would also fully disable the electronic brake-force distribution (EBD) and cause the rear wheels to lock up prematurely so you wouldn't want to do it for track days that involving turning at speed.

When I was testing different options to disable the ABS-based traction and dynamic aids on the ST it appears that if you disconnect a rear wheel ABS sensor the EBD function is still active but I'm guessing at a default proportioning ratio. Under hard stops you may get some premature rear wheel lock-up but it didn't seem too bad to control with threshold braking.

As for gains at the track, by disabling the ABS you'll lose the torque vectoring as well as the active understeer control. The chassis goes from really playful to a slightly limp, understeering mess (my opinion based on some back road testing). It appears the overall suspension tuning was designed with the electronic brake-based chassis aids playing an integral role.

I'm sure we've got quite a few people who've been tracking the car as both ST models have been doing well in stock auto-x classes and they might be able to offer better advice or have experimented with the setup. I have a feeling that if you're doing track events an ST with an otherwise stock suspension will likely be quicker with the system enabled, and if you're getting overheated brakes might benefit from a set of aggressive track-only pads installed at the track (with proper warm-up) and frequent brake fluid flushes and bleeds with a high quality race fluid.
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I really enjoyed this post... While I don't quite understand all of it... I can tell you that I do however notice the difference in the 3 different driving modes. With it in normal mode, engine engagements are much jerkier and the gearbox feels more "notchy". In sport mode, launch is much smoother and gear engagements are much more fluid, while ESC off feels mostly like sport mode... I do notice that there is almost no sense of engagement of the clutch while shifting and that the steering seems very loose.
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