E90. ABS/DSC problem

Today an interesting diagnostics case appeared. The owner of the car complained, that driving with speed over 70 km/h, sometimes problems with ABS/DSC appear. When the appropriate symbol in KOMBI light up, the car starts to brake chaotically, the engine decreases power.

 

Checking the error message list with INPA, we have to conclude, that everything is OK. At least in the comprehension of the ABS/DSC module.

Next step – driving session with the observation of live data. The problem became clear for several minutes. Here, the turning speed of all four wheels during a driving session:

As we see, all wheel speed sensors are reading data, speed is averagely the same. But the readings of the left/rear wheel are jittering more than for other wheels.

The cause of this jittering is problems of the performance of ABS/DSC.

When the guilty wheel has found, it already becomes easier: the axial and radial play has to be checked, also the tooth-wheel of the ABS sensor has to be checked. If there is no play and the wheel of a sensor is in good order, the sensor itself has to be replaced.

 

The topic of this entry – also this case goes into a category when specialists at BMW AG dealer centers would not be able to repair correctly. Why? BMW AG dealer centers are not allowed to use INPA. ISTA, instead, displays the wheel turning speed as only (very small size) numbers.

You can make sure of yourself, that the displaying of turning speed without bar don’t allow to identify the damaged wheel. See the final part of the video, displayed in this entry. Data of all wheels are changing rapidly enough, even checking the changes in data, it doesn’t become clear, where the problem can lie.