SRS Light has me puzzled

[RES]

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.

[RES]

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?

[Kebowers]

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.

[blackmercedes]

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.

[RES]

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?

[pcmaher]

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.

[RES]

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

[pcmaher]

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.

[Lou II]

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

[Jim B.]

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

[JimF]

Originally Posted by pcmaher

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. .

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! So far so good but time will tell. . . .

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

[pcmaher]

Hi Jim,

Thanks for the info.