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First I'd just wanted to thank the forum and recognize all the help that many of you have been providing to new W211 MB owners like me over the years. I have done an extensive research on all the SRS-related topics that were posted here that date back to 14 years ago before I posted this question. I wanted to make sure I wouldn’t post a question that had already been previously answered.
My problem is an SRS light that came on after I tried to diagnose a parasitic draw test by running my voltmeter through the negative battery cable. Out of ignorance, instead of either using a better voltmeter with a fuse or with 20 amp capacity, I ran a cheap one directly through the negative cable thinking it was safe. Doors were latched, hood and trunk were latched… however, I pulled the door by the handle and it triggered the keyless entry, causing a peak in current over 10 amps… You can imagine the disaster.
As the result, the RF amplifier fuse blew out, the lower command unit fried and caused the electrical to go haywire and everything in the car light up like a Christmas tree… and yes, the SRS light came on.
After I removed the lower command unit (bought a new one from ebay) the car went back to normal. However, I now got the SRS light on, and by further inspecting the DTCs, it is on due to driver side airbag squibs, and both front ETRs resistance being too high. The reason I described the event is so you don’t ask of the car has been in an accident. The error appeared because of a short.
So now I need to figure out whether I need to replace the airbag and the ETRs; Or if I need to have my SRS module reset and/or fixed to clear any hard codes.
What I've already tried so far:
Tried resetting the SRS through MBII. No success because it's still saying that the resistance is too high got the squibs (I guess that means that the circuit is open, right?)
Removed the airbag and tested the resistance of the connectors. It read 0.2 in the 200 ohms scale. I don’t know if that's normal.
Replaced the lower control module, but looking at the SRS wiring diagram, it only has one wire going from the SRS module to it. I think it's just for the passenger side airbag light that goes on and off depending is someone is occupying the passenger seat.
Cleaned the negative terminals for the battery and for the engine fuse box.
Have any of you had a similar problem with the driver airbag and ETRs after a short? Do any of you have any ideas on how to try to narrow down whether it's the SRS module or the airbag/ETRs? Any help if appreciated.
I was able to resolve my SRS light on problem after a lot of investigation. As I mentioned on my previous post, the SRS light came on after my lower control unit malfunctioned. After replacing the LCU and I could not reset the SRS light with the iCarsoft MB2 reader. I kept saying that the airbags and the ETR squibs had resistance too large. I did several tests with the squibs and even got a different SRS module at the junkyard to test if the error would change. We came to the conclusion (I had help from Lou Palomino mercedes Tech) that it was the reader that was reading a false positive error.
I took my car to the dealer and after paying the $99 diagnostic fee, they were able to reset the SRS DTCs. So lesson learned... icarsoft is crap and I returned it. I'll invest in a good OBD reader that can work on mercedes.
I will post a video on my channel soon about the process. Subscribe if you want to see the video -> youtube.com/dcfgarage
Yes, the SRs light was on in the IC. I had 11 DTCs in the SRS module, but they were all stored. icarsoft was also reading that the driver airbag squibs and both front ETRs had resistance too large, when it was not the case.
Icarsoft was reading something in the data stream that did not exist (AKA false positive). I've done the diagnosis and came to this conclusion after extensive testing with an experienced MB technician.
If my car had any real faults with the SRS system, the dealer would not have been able to clear it. Makes sense?
And the SRS light was on because of the sored DTCs that were generated by the electrical malfunction. Since all the DTCs were only stored and not current, the MB2 reader should have been able to clear it.
