Need help with SRS (airbag) problem
 

'88 190E 2.6 five-speed,(California model) 83K miles

After six months of storage the SRS light is on. Upon start up it goes off and then comes back on after a few seconds. I don't have too many start cycles on the car at this time. Sometimes these systems will turn off the indicator if the fault does not repeat for the next 25 or so power-on cycles, but I probably only have about a dozen.

I have the electrical schematic (from what I believe is a complete set of digital service manuals that I have) and it appears that the system looks for an "impulse readout", which may just check whether the electronic control module is functioning. Does this system have any diagnostics?

It's not clear to me where to start troubleshooting, so I would appreciate comments from anyone with experience troubleshooting an SRS light on condition or any references to a more detailed troubleshooting procedure for the system.

Duke

Begin by replacing all the fuses, they don't age very well. Have you tried putting your seatbelt on?

For a 1988 - 1993 W201 you can read diagnostic codes from sockets 1 and 6 on X11/4. If you don't have a code reader you should be able to short the two sockets for 2 to 4 seconds, with the ignition on, and then read the flashes from the SRS instrument light. The codes are:

1 - No fault
2 - SRS control module ()N2/2)
3 - Driver air bag
5 - Driver seat belt buckle
6 - Front passenger seat belt buckle
8 - Voltage supply (circuit 15R)
9 - Warning lamp (A1e15) defective
10 - SRS - Control module (N2/2) was activated

To erase the codes, short the sockets for 6 to 8 seconds. Note you must erase each code individually.

You may not be able to erase code 10.

Thank-you!!! I was hoping the system might have some diagnositics.

It might take me a few days to get around to running the diagnostics, and I will definitely let you know the results.

I looked at my pdfs of all the service manuals again and I could not find any specific procedure to test the SRS or R&I SRS components. Can you give me a manual title and section number? I assume that's where you got the diagnostic codes. Thanks, again.

Duke

Page 254: http://www.w124performance.com/docs/mb/diagnostics/DTC_Reference_Guide_Ed.B.pdf

Excellent! I've added this to my digital shop manual collection. I should get around to running diagnostics in the next couple of days... will report back on the results.

Duke

...finallly got around to running the diagnostics.

After a few false starts and getting the hang of how long to short the pins to read and erase codes, I'm getting a consistent code 2 after mulitple erases and reads - not good - that's the control module, which is likely very expensive.

It's located on the transmission tunnel below the radio, so I'll have to get in there and check and cycle the connector to see if that does the trick.

From the circuit diagram it appears that the SRS is hot wired directly off the ignition switch rather than a fused circuit, so something simple like a fuse is probably not in the cards.

If anyone has had to deal with the SRS control module, please let me know the deal.

BTW, receptacle 6 is deep in the X11/4 connector. (At first glance it looks like there is no receptacle at all in position 6.) My test probe wasn't long enough to reach it, so I rounded off the point of a galvanized roofing nail and used that as as a probe extender.

Duke