Make your Move

ESC or Electronic Stability Controls are going to be a standard feature on 2012 and newer cars.  Learning what is all involved in these systems is going to be very important for every tech out there.  These ESC systems come under different names with different manufacturers.  GM StabiliTrac, Ford AdvanceTrac, Chrysler’s Electronic Stability Program (ESP), Dynamics Control (Subaru), Dynamic Stability Control (Volvo), Vehicle Stability Assist (Honda), and Vehicle Stability Control (Toyota).  Although they have different names they all basically do the same thing.  In a simpler term it all comes down to “intervention braking”.

What is intervention braking?  It’s a way to allow the driver to regain control of the vehicle under most/or any circumstances.  This is accomplished with the ESC module reading and interpreting all the other systems information in the car.

Like in a chess game, the King is the piece that is the key to survival in the game.  For a decade or so the PCM was always considered the King.  However, the PCM has to take a back seat to the ESC these days.  The PCM’s (Power Control Module) main purpose is to dictate the reactions of the driver’s responses and control emissions; the TCM (Transmission Control Module) dictates the action of the transmission; the ABS (Anti-loc brake system) determines brake use, so on and so on with all the various computer systems in the car.

With the idea that we need to have more preventative control of the vehicle the ESC systems have to be given credit where credit is due.  Even though each of these different systems do talk to each other and perform their task well, it’s the ESC who stands out as the King piece in this chess game of vehicle mobility.  Everything in regards to the operation of the vehicle has some bearing on the ESC system.  Mind you, we are talking about an intervention with regards to the overall control of the vehicle in either emergency situations or in regards to weather conditions or the angle of the car. (At least the glove box door isn’t part of it… yet…)

How is this Accomplished?
The ESC systems takes in account, wheel speeds, steering angle, angle of inclination, front to rear sway, weather conditions, and many other factors.  Complicated yes, but once you break down the individual sensors that are involved it can be quite simple to understand.

Take for instance the pawns in this chess game: the wheel speed sensors.  The ESC takes its needed information from the ABS unit and will determine if there is a need to bring the car back under control.  This could be an under steer condition, over steer condition, or even a snow plowing condition such as when the wheel is turned sharply but the wheel speeds are different.  It can see all of this with the help of the steering angle sensor and various other control sensors.  If one of these situations is present the ESC will direct the ABS to start braking the appropriate wheel to regain control.

Factors to Consider
One of the other factors the ESC will look at is the wiper switch activation or with some sort of humidity indicator.  These signals will tell the ESC of a condition that might reduce brake efficiency do to the weather.  The ESC has the ability to tell the ABS to pulse the brake pads against the rotor about every 90 seconds or so to dry the brake rotors off.  (Brake drying).  Not to make this even more complicated, there is also an algorithm for brake temperature coefficient values.  The computer knows the type of material used in the brake pads from the original manufacturers and if it feels you are reaching a critical point where brake fading may occur it will unlock the calipers and allow the pads and rotors to cool off before reapplying the pads against the rotors. 

Inclines and Rollovers
Let’s say you’re on a steep incline and you have the car in drive.  An inclinometer or accelerometer will measure the angle and determine that you don’t want to roll backwards.  In this case the ESC commands the ABS to hold the brake pads against the rotor and only allow the car to roll forward once it sees the gas pedal being depressed.

Along with the condition where the rear of the car is moving out of alignment or the side to side tilt is greater than its programming the YAW factor sensor now becomes the next pawn in the game and the ESC uses that information to determine if the brakes need to be applied. There’s even an algorithm for “anticipated braking” this is where the ESC sees you have taken your foot off of the accelerator and makes the call that your next move is to apply the brakes.  The ESC will tell the ABS to move the pads a bit closer than at their rest position for a much quicker brake response.  This also applies to emergency braking.

  Again, the ESC sees your reaction time from the gas pedal to the brake pedal and will apply the brakes harder and quicker than your foot can react.  Hopefully to avoid any conditions that could be fatal for the driver.

On some models this also involves the backup sensors and crash avoidance systems. There’s a lot more involved than just sensors as well, engine rpm, what gear the transmission is in, and what speed you’re traveling.  In some cases the reaction time or sway (roll over condition) of the car can also induce an action from the ESC to drop spark timing or injector pulse to slow the vehicle back down to a controllable level. 

My first encounter with an ESC system was on a 2009 Pontiac G6.  The customer’s complaint was the traction light and ABS light would come on periodically.  Anytime this happened the brake lights would stay on.  In order to make this repair you’ll need a Tech II (or equivalent) to read the brake on/off signal.  In this case when I did manage to see the failure the brake light command was stuck on.  The only way to get it to turn off was to disconnect the BPPS (Brake Pressure Position Switch).  Replacing the switch was only part of the answer.  Once the switch is replaced it also needs to be recalibrated to the vehicle.  The BPPS ratio and the BPPS learned home must be equal. This is accomplished by using the Tech II scanner and perform a BPPS calibration.

But, I’m not done yet.  On the very next test drive the lights came back on and so did the brake lights.  However, I did have an on/off signal for the brake command this time.  But, the BPPS ratio and learn home mode were out of sync with each other again.  (Even after repeated recalibrations). Seems there is a service bulletin on intermittent brake lights that do not function correctly.  (Reference number 08-05-22-009C).  The service bulletin describes how to add dielectric lubricant to the connector pins of the BCM with a nylon brush to treat the pins against fretting corrosion.

After following the service bulletin there were no other problems with the system.  I’ll call that a checkmate in my book.  A couple of drive tests confirmed the repair.  I didn’t see any mention of the traction light as an indication of the brake light problem anywhere in the diagnostics but service bulletin did mention about certain codes that affected the traction control.  The chess game continues: I’m sure the manufacturers will be adding even more prevention controls to the ESC in the near future.  My advice, find out as much information as you can on these systems and study them well.  They’re not going away… there here to stay.

The sad part for me is that there will no longer be any tire spinning, car sliding, or donuts in the high school parking lot.  (Yea, I did my share of that back in my day.)  Because, the ESC systems prevents that from ever happening with the technology developed for today’s cars.

Due to the constraints of what is possible to put into one article it’s not possible to cover all the features of the ESC system.  As technicians, all we can do is learn these new systems and prepare ourselves to diagnose and repair them.  It’s a chess game for sure, but all we can do as a modern service technician is to wait for the manufacturers to make the next move.