Electronic stability control on 2017 Grand Cherokee

Question

My 2017 Grand Cherokee is equipped with electronic stability control. According to the manual, the idea/intent is to apply selective braking and reduce engine power as needed to keep the car on its intended path.

The annoying thing is, it kicks in while cornering on dry pavement. Typical example: stopped at an intersection to make a left turn from one wide (2 lanes each way plus turn lanes) road to another. When you get a chance, you want to make the turn promptly, but about halfway into the turn, the ABS starts buzzing, the engine loses power, and it really slows down, to the point of being scary because I'm in the path of oncoming traffic. If I turn off the ESC, I can take the corner no problem. Never notice it on right turns even when taken quite quickly.

This leads to a few questions:

Why does it only happen on left turns? Is it a geometry/physics thing or could there be sensor issues?

Why does it kick in at all when I know I can make the maneuver safely at a higher speed - all four wheels firmly planted at all times? Again, could it be a sensor issue, or overly conservative thresholds in the system?

Do I just have to live with it (and get in the habit of turning the thing off) or is it something that can be fixed or adjusted? I know it would be "nice to have" in an emergency maneuver, so I would want it on as much of the time as possible, just not fire up in routine driving.

Answer 1

It sounds like a steering angle sensor issue.

The ESP/ABS ecu uses the steering angle sensor to determine where you are pointing the steering wheel. It then looks at each wheel speed value, it can determine what direction the vehicle is traveling in by the wheel speeds, if this is different to the steering angle sensor the ESP kicks in.

What can happen is that the steering angle sensor is out of calibration, not so much that is implausible or detectable but just enough so that in certain conditions the values aren't right and you get the symptoms you are experiencing.

A common mistake made by technicians is to calibrate the sensor to the angle of the actual steering wheel rather than the front wheels. So in other words they make sure the steering wheel is dead straight and calibrate the sensor while what they should do is to drive the car in a dead straight line for as long as they can and then calibrate the sensor. Obviously the best way would be to use some dead accurate tracking/alignment gauges to confirm the alignment and calibrate the sensor at the same time.

A way to confirm is to monitor the live data the ESP ECU is seeing, have an assistant drive in a dead straight line and monitor the steering angle value, ideally it should be 0 or 360 depending on how the ECU interperpates it. Also monitor the wheel speeds, they should all be the same.

It most definitely can be fixed/adjusted, as a quick fix the technician can drive in a long straight line on flat level ground and calibrate all necessary sensors. There will also be ride height sensors so these should be calibrated to. If that cures the problem then all well and good but I would then fully check all of the alignment, camber, tracking etc and if this has to be altered then calibrate the sensors again.

Answer 2

I can't be sure, but I can tell you from Subaru "tone wheel" experience that just a little bit of rust or debris can cause some really odd behavior.

The sensor consists of a wound coil with a voltage passed through it. The voltage is modulated by lumps of steel passing through the resultant magnetic field in something referred to as a "hall effect".

Honestly, despite the fact I'm an eternal geek, I don't fully understand how it all works. BUT... I will tell you the sensor accumulates ferrous debris (rust) particles, and those are not good and make random sensor signals which confuse the ABS/traction control computer inputs. It's not hard to imagine with metallic brake pads operating in close proximity.

Also, in the case of Subarus at least, the "tone wheel" (it's kinda like roulette on a wheel bearing) can degrade and rust such that the teeth are not consistent. The computer is expecting a constant pulse pattern; when a tooth is rusted away it sees a "gap" and assumes the wheel is locked.

Sometimes the tone wheel is part of the bearing cartridge, sometimes it's built into a CV halfshart. In any case, it has to be clean and pristine to work properly.

SO... I'd have those sensors checked out with a proper scan tool (you can just spin the tires by hand while on a lift) before I made any final judgements on your path forward.

On my 1997 Subaru Impreza with 200K+ miles, I pulled the ABS fuse... But that's just cheap old onery me...

Good luck!