ABS / DSC fault

[Dave Ett]

Hi All,

Recent subscriber to this forum, having been on a UK one for a while now. Had my E53 a couple of years, having owned a variety of 5 series over the last 20 years.

So, the problem:

I have the ABS / DSC lights on, so plugged in INPA to see what's up.

Pressure sender interference triggered 248 times, and steering angle sensor once.

I'm guessing there's a pressure issue! The steering one cleared.

Having read loads on the subject I did some more checks (what a sod it is to get to) and it does seem to be a sender fault:

The voltage varied about 0.2V between brake off and hard on, and INPA showed these:

Firstly brakes off:


Then brakes on as hard as I could:


Assuming I'm reading it correctly, the pressure barely rises.

Anyone confirm or contradict this diagnosis?

[wpoll]

Voltage? Are you referring to the cross acceleration value? Measured in meters per second, per second?

I'm not 100% sure about all these readings but it appears that the value labelled cross acceleration is an acceleration sensor (or deceleration when braking) and I wouldn't expect it to change when the vehicle is stationary. I'm assuming you took these reading while the car wasn't moving.

The value labelled print is measured in bar, meaning its a pressure and it is certainly changing when you apply the brakes (from zero bar to 39 bar, which is a lot of pressure!!)

[Dave Ett]

Hi wpoll, thanks for your response.

I read through this bunch of info here:

Brake Pressure Sensor (DSC/ABS/BRAKE Trifecta) - Bimmerfest - BMW Forums

Which says the brake pressure can get up to 250Bar, which I assume explains why the bar on INPA can get up to 300.

I was stationary yes, so ignored anything else like cross acceleration.

I've got a new valve to install this evening (cheaper from the dealer than on-line too) so hopefully I'll be reporting it's fixed, or adding my name to list of other's who spent a fortune on parts which didn't fix the problem!

[wpoll]

Had a quick read over the BPS thread you referenced - will read in more detail when I get home but wow - there's a lot to digest in there!

Your diagnosis seems to indicate a faulty sensor, so you could try another sensor, if its way cheaper than an ABS module repair. I don't see an easy way to eliminate the sensor other than replacing it.

[Dave Ett]

Sadly, there is still a problem. Initially the lights went out and I thought "YAY!".

Then they came back on after about 5 miles. Flickered on and off a few times, then stayed on steady. Each time I switch off a leave the car for a while they go out, and come back on after 5 miles or so.

INPA now shows the pressure sensor as giving a full-scale output all the time, which is very odd. Doesn't change at all with brake pressure. Clearly more invest to do, but suspect it's time to pull the ABS control module and send it for testing / repair.

Could be a faulty new sensor of course, so I will check that before I pull the module!