SRS Light has me puzzled
 

1995 C220. SRS light stays on for a minute after starting car. I purchased a TRISCO PS-411 scanner to trouble shoot the problem. Read codes 24, 139. Replaced drivers side seat belt switch. Erased code but light stays on and code 139 comes back. I am puzzled by code 139. It is not on the list for the SRS function. Problem seemed to occur after I put a large heavy box on the folded rear seat. After doing a search on this web site, I checked resistances on the old and new seat belt switches. They both read the required normal values latched and unlatched, so it seems that the original switch was OK.

According to the TRISCO technician the 139 is a miscode. He seems to think that the car is not producing enough voltage to turn the light off. What is normal and how can I check it?

flaky seat belt light
 

might it be the weight sensing switch in the rear seat is damaged and closed, telling the system that seat is occupied? Try latching the rear seat belts to check.

A 1995 W202 has no occupancy sensors in the rear. There are no air-bags or ETRs in the back. Putting the rear seat down in the folded position has nothing to do with it.

Is there a way to check the seat belt tensioner squibs. There is a third connector under the seat in addition to the two from the seat belt latch with four contacts on it. What is its function?

It could simply be a coincidence that the SRS light comes on now, after the package in the rear seat. I have a 95 S600, and the SRS light comes on immediately after starting the car, and goes out after 1 second or so as it should (the SRS light should stay on a little longer than the rest of the caution lights). It then immediately comes back on. My Trisco scanner tells me that the front passenger seat occupancy sensor is bad. I haven't changed it yet, as this is Low Priority (LP) for me.

PCMaher. Does your light go off again after a minute or so?

Yes, I should have included that info in my previous post. Sorry about that. The light goes off after about a minute, and stays off until the next time I start the car.

Been a while. Did you ever resolve this problem? Same symtoms in my '94 SL 320.

Airbag contact rings and brushes maybe? Just wondering...

Pete, found your post this morning while looking for posts with a similar problem as mine. The SRS comes on after doing a system check and then goes off in a minute or so of driving.

Used my tech's AST Retriever to diagnose the exact same problem as yours but I used some "Radio Shack Color TV Tuner Cleaner" sprayed into the driver's seat beat connector. Then used compressed air to clean it out. My tech said the 'micro-switch' get dirt/dust and causes an open connection. So BION, that fixed it! :D So far so good but time will tell. . . .

Something for you to try if you haven't fixed yours . . . .

Hi Jim,

Thanks for the info.