For the last 2 or 3 months I've been having a problem with the active handling on my 02 A4 C5.

The problem has no particular pattern, I've only notced it at speeds over 50mph.

Here's whats up...If I engage cruise control at any speed of 60mph and over... after a few minutes even seconds there is a voltage drop of about 1-2 volts, the cruise control automatically cuts off and "Active Handling" reads out on my DIC. This occurs sporadically..

Then I have a more serious problem that makes me quite nervous... all of the above problems happen along with the rear driverside wheel slightly locking up on its own. The brake applies enough to jerk me out of my lane... this does not ocur everytime... but probably 1 out of every 6 times the other problems occur.

There are no check lights or codes showing... I've gone to the dealership twice and all the can tell me is that without a code they cant help me.

Could someone please tell me WTF is up??

 

That is really strange that a code isn't showing. My first thought is a wheel speed sensor acting up or electrically bad connection to it.

 

If active handling engages cruise control is shut off so lets assume the cruise is a symptom and not a cause. You mention a voltage drop of 1 to 2 volts. I don't know how you are measuring the voltage at the time it occurs but the ABS pump (AH is part of the ABS system) can draw a lot of current which can cause a quick voltage drop.

There are several things that might cause the condition. One of them is wheel alignment. If the system senses the car is turning and isn't responding quickly enough it will apply a brake to cause the car to yaw in the direction it thinks you are turning. In your case you say the driver's side rear brake is being applied which is an indication the system thinks you are turning left and the car isn't yawing fast enough (understeer) so it applies that brake. If your alignment is out so the steering wheel is turned to the left you might get a reaction like this. Usually the system will trigger a code but you may be on the hairy edge. The second thing that can cause this problem is the steering wheel position sensor. Again usually a code is thrown but sometimes not. Another sensor that could cause the problem is the yaw rate sensor. It is located under the radio and if its been moved it could throwing erroneous signals the system wouldn't know were erroneous. There are other things to check as well but these are the first three I would look at.

A competent tech should be able to figure out what is happening and fix it.

There are ways to check these things yourself but involve using a Digital Multimeter and making some voltage measurements. I can e-mail several procedures to you as posting them all would take a lot of space in this thread.


Bill

 

Mine was doing the same thing. Threw a code for steering wheel sensor.

 

My '99 threw a code for the steering wheel position sensor but only when going over bumps and so on. It never caused the Active Handling to do anything, although that was an earlier deisgn of that system. The yaw rate sensors/accellerometers were under the passenger seat on the '99 and if they are still there on your's, you might want to insure the connectors are dry and tight....but I would imagine a code would be present.

 

I've heard that if your front and rear tires are within 1/2" in diameter (the rears are supposed to be taller than the fronts) the brake locking thing can happen as the active handling system reads this as slippage and is trying to correct it

 

That causes activation of traction control as both rear wheels appear to be slipping and the brakes would be applied to both. He is getting application of just one rear brake so that indicates a possible activation of active handling which isn't a function of traction control.

Bill

 

Listen to Bill D's advice cause he's 100% correct!

Unless you dig into this systen and logically troubleshoot it, you could be spending a lot of unnecessary cash. The EBTCM is getting information from something telling it that it needs to apply the brake/s. You just need to figure out what that sensor is.

Other than a serious alignment issue (Is your steering wheel pointing straight when the car is driving straight?) the sensor in this system with the highest failure rate is the Steering Wheel Position Sensor (SWPS)

Anyone with a TECH II including the dealer can check this entire system out and see where the bad signal is coming from. You just need to provide them the necessary information (Driver Diagnoistic Information) so that they know where to start looking.

Keep us up to date on how you make out.

BC