dhoffman31

The ESP flashes on and engine rpm drops when I accelerate moderately or faster at almost any speed. My mechanic found no stored codes and went through the procedure to zero out sensors and reset values. Car runs normal when I manually shut ESP program off with the dash button.

Still have the same symptoms where the ESP kicks in when it is not suppose to. Mechanic says he can't do much without a code. Does any one know of other things to check or what could be causing this?
Dan

silverd2

What year/model and mileage?

Apparently it really believes it needs intervention, so not throwing a code.

I'm no expert, but might want to check and clean all 4 ABS sensors at wheels and visually check ABS slotted rings on CV joints through sensor holes for clean/undamaged slots, while the wheel speed sensors (ABS) are out. Car could be misreading wheel speed (?). Easy job and maybe a good place to start. Will clean up with regular spray brake cleaner.

Have you hit brakes hard lately on wet pavement or gravel...witnessed correct pulsing ABS?

This is just a semi-educated guess and starting point...for all it's worth.

dhoffman31

It is a 2001 A8L with 144k on it. I did have to stop fast recently and the ABS kicked in. I think your right about it thinking a wheel is spinning. Maybe the slotted rings need cleaning. I'll check
Thanks for the feedback

Nurburgringer

If the ABS works fine, then it's probably not the wheel speed sensors. I would find some gravel or snow, and do an ABS stop (where you have plenty of room if something goes wrong). If the ABS stop doesn't jerk you from side to side, then you can probably rule out the wheel speed sensors.

Next thing I would ask - does this happen more when you're turning while accelerating? Does this happen if you make a tight turn, without hard acceleration?

If related to turning, then you want to be thinking about the yaw rate sensor, lateral accelerometer, or the steering angle sensor.

If not related to turning, then it is your longitudinal accelerometer and what you're seeing is a traction control activation. (I'd bet lunch its something in this direction)

Either way - I would focus debug efforts on those four sensors - might be worth trying the re-zero procedure again.

Another way to narrow it down to the longitudinal accelerometer is to see if accelerating uphill or downhill make the situation worse.


Nickel version background: AWD cars with traction control systems, especially ones with torsen centers, cannot rely on the 4 wheel speed sensors to determine vehicle speed. If it did, and you were on ice... all 4 wheels would spin up simultaneously and you'd have no traction control. So, it uses the longitudinal accelerometer to compare the acceleration of the 4 wheels (usually the acceleration of the slowest wheel though there is some trickery in there if it knows you are turning) to the longitudinal accelerometer. IF wheels are accelerating faster than the long accel, then traction control kicks in and reduces engine power.

cj750rock

[QUOTE=Nurburgringer;24105274]If the ABS works fine, then it's probably not the wheel speed sensors. I would find some gravel or snow, and do an ABS stop (where you have plenty of room if something goes wrong). If the ABS stop doesn't jerk you from side to side, then you can probably rule out the wheel speed sensors.

Next thing I would ask - does this happen more when you're turning while accelerating? Does this happen if you make a tight turn, without hard acceleration?

If related to turning, then you want to be thinking about the yaw rate sensor, lateral accelerometer, or the steering angle sensor.

If not related to turning, then it is your longitudinal accelerometer and what you're seeing is a traction control activation. (I'd bet lunch its something in this direction)

Either way - I would focus debug efforts on those four sensors - might be worth trying the re-zero procedure again.

Another way to narrow it down to the longitudinal accelerometer is to see if accelerating uphill or downhill make the situation worse.

Mine happens when turning slightly at any speed above 50mph. Where is the YAW sensor?

silverd2

"....Where is the YAW sensor?"

Here ya go...right next to the transverse accel sensor >>>

Prospeeder

Dont forget to rule out the possibility of a bad ABS/ESP control module. From what i have seen almost every VW/Audi with ABS has the possibility of failure. Some much much more than others. And of course, if the module itself is having an issue, sometimes it is not aware of it and thinks its normal.