Colleagues,

I have a recurring problem with my BMW 740iL that I believe recurs because BMW service is treating symptoms (or fault codes), and not the true cause. If you know the heart of a BMW and want to offer your opinion on the true cause of this problem, please read the details below, and give me your opinion.

I have a 1999 740iL and have had 7 events in the last 42 months in which while driving on normal roads, the DSC indicator light came on, the brakes were applied without my pressing on the brake pedal, and the car was taken to a stop. Once stopped, I could not move the vehicle in either forward or reverse.

1. The first event occurred in January 2004. After the first event, the dealer replaced the master cylinder.

2. One year later, the same thing happened and they repleced the brake pressure switch. They also found a "dead" battery and replaced it.

3. 13 days and 335 miles later, the same thing happened and they replaced the master cylinder again.

4. 6 weeks and 1480 miles later, the same thing happened and they replaced the ASC Hydro unit and the pre-charge pump. In between these events, the battery was replaced for the second time.

5. One year later and 9500 miles later, the same thing happened, and they replaced the master cylinder (third time).

6. Fourteen months later, the same thing happened, the car was in the shop for more than a month. Service manager called me and said they had been brainstorming the issue, talking with BMW EU service, and could not figure out what it was. They then drained the brake fluid, said they found some contaminant in it, installed a replacement ASC Hydro unit, and it supposedly worked, but refused to cover any charges. When they replaced the original ASC Hydro Unit, the car ran normally. We took the vehicle. Oh, by the way, the battery was replaced for the third time.

7. 3 weeks and ~500 miles later, the SEVENTH malfunction occurred. The dealer refused to take any responsibility.

Within 24 hours of this last event, research at e38.org, bimmerboard, bimmerforums and elsewhere led me to what I believe has been the problem all along, and has been missed by BMW service.

I would post my theory, but I don't want to limit anyone's analysis.

What do you think it is, and what do you think I should do with BMW?

Thanks,
cwfarley

we have a few bimmer techs who drop by here, hope they'll chime in. IMHO, way overdue to take your car to a different dealer...i admire your patience!

i would have traded it in the first time that happened. . .what a scary thing to have happen.

what is your theory? it almost sounds like the ECU thinks that you have wheel spin so maybe check wheel sensors. dunno

A malfunction of the DSC subsystem, is the most likely cause of the repeated malfunctions If reducing the throttle, then retards ignition timing don't make the DSC control unit happy (agreement of signals from rear wheel rotation sensors), the rear wheel brakes are applied, increasingly as necessary .
A malfunction of this subsystem could result from either intermittent malfunction of one of the wheel rotation rate sensors, repeated malfunction of one of the sensors (although very slight) producing erroneous adaptive control conditions in the DSC control which are exceeded when the sensor functions correctly, problems with the wiring harness connecting the sensors to the DSC control unit or problems with the electronics in the DSC control unit.
By the way, after making the same post to bimmerboard, got 2 opinions pointing to DSC control, sensors, or wiring within 2 hours, including one which relayed that a number of 99 owners have had problems with the DSC control unit when it gets hot under the hood.

Craig

kwel :)

Did you, or have you, ever considered the possibility that the car, DSC, is doing exactly what its supposed to do? Bail out a driver that doesn't know how to drive.

Between bimmerboard and bimmerforum, the tally is

Between bimmerboard and bimmerforum, the tally is
DSC-8
Driver-1

It is either the wheel sensor array or the ABS system.

The ABS receives wheel speed data first and shares it with the other systems that need to see it (like cruise control, DSC, DME, etc). Either the ABS control is shot or the wheel sensor array is sending faulty or imtermittent data.

If the ABS suddenly doesn't see wheel speed data, it may go to a default stop mode. Have you examined the condition of the wire harness that connects the wheel speed sensors to the ABS?

If the wire harness is OK then I'd look at the ABS itself.