: 2008 550i throwing Passenger Restraint System Error - replace Main Wiring Harness?!

06-15-2012, 07:18 PM
Hey Everyone,

I spent a lot of time on this forum when I was researching and buying my 2008 550i - and have a deep appreciation for the depth of knowledge available here. My car has been completely awesome to own and drive and almost completely trouble free. Right up until the last 6 months... when I encountered the evil "Passenger Restraint Warning."

The warning message started in December and the dealer has tried to fix it 3 times - we're now on attempt number 4. The dealer has replaced the driver-side air bag sensor (twice) and the main air bag control unit. The tech say the wiring and connectors are working ok.

Now the dealer says there must be a fault in the Main Wiring Harness and wants to replace that. This has me very concerned. The dealer say it will take 10 days to get the part from Germany and another 10 days to do the work. Which sounds like major surgery to the car --- and I am worried that it will never quite be put back together again.

I'm really concerned that the car will simply never be the same after this level of surgery and the car will be off warranty after this and I'm concerned about ongoing maintenance costs.

Does anyone have experience with this? What is involved in this - how much of the car is dis-assembled? Does this sound like a reasonable solution to this issue? Will this doom the car to endless electrical issues?

e39 dave
06-15-2012, 07:46 PM
I have an '08 550 also. I noticed a couple of weeks ago that the "passenger air bag light" was on (it is near the sunroof switch). Then a while later, it was off. I happen to take my car to the dealer a few days later for an unrelated issue. While the car was there, I had them check the the passenger air bag issue. The SA told me that the tech checked the car and there were no faults to be found with the passanger air bag. As far I know my passenger air bag is functional.
What symptoms are you having with your car? Do you have the warning light on near the sunroof switch?

06-15-2012, 08:48 PM
I bought my '08 550i last year and had the same issue crop up about 3 times. The last time they recommended changing the wiring harness and required a long wait for the part to come in from Germany. As it was just covered by warranty and they felt it was a safety issue, my dealership offered a brand new X1 as a courtesy while they sorted out my car. They had the car for about a month and since then I have not seen the issue return. I haven't noticed anything majorly different about the car.. no loose panels.

06-16-2012, 12:37 AM
@e39_dave - The warning message comes up on iDrive - takes over the whole display. Someone posted a picture of it on a thread some time back. I have not noticed an airbag light near the sunroof switch. There has been no other issue that is noticeable with the car other than the warning message on iDrive.

@loungin - thanks for the feedback on your experience. Makes me feel a lot better about having them replace the main wiring harness. It is covered with the warranty - so direct cost today is not the issue, more a concern about what fallout is possible in the future after major work like this. Good to hear that you haven't noticed any issues after you had it done. How long ago did you have it done?

06-16-2012, 12:22 PM
I had the work done not long ago.. in the spring of this year.

06-16-2012, 02:24 PM
Thanks @loungin.

If anyone can help me troubleshoot this - here are the fault codes and diagnostic codes that the Dealer reported:

First time in:
faulty front air bag sensor diag.. D6577_00000000_25_002 verified. found fc 93C8ACSM/MRS: Airbag front sensor, driver's side.. performed test plan.. found module ok.. power and ground.. per diag.. removed front bumper.. replaced driver sensor.. ok now.. cleared all faults.

Second time in:
Internal failure in air bag control unit verified complaint. Performed ist a vehicle test. interrogated fault memory. found fault in ACSM-MRS:93C8 air bag front sensor, driver side. performed test plan. as per test plan inspected all wiring and connectors to left front airbag sensor. found all wiring and connectors check out ok. found internal failure in airbag control unit.
diag code:d6577_acsm0000_90_002. replaced airbag control unit.
program/encode complete vehicle with ista/p:46.5.000 and cas.

Don't have any notes from dealer on 3rd time - and vehicle is now in for 4th attempt.

Any thoughts on Fault Code "ACSM-MRS:93C8"?
After 4 attempts to fix and requiring that half the car be taken apart to do the work, does this enter "lemon law" territory in California?