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  #1  
Old 04-15-2018, 08:52 PM
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'99 E300 W210 SRS light on

My friend's '99 E300 has the red SRS light on the cluster lit. Is it possible that a seatbelt switch is bad? If so, anyone know how to test it? The OBD2 was checked for codes, and none are present. Fortunately a parts car is available.

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Old 04-15-2018, 09:11 PM
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SRS generally has to do with airbags. Broken clock spring in the steering wheel?
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  #3  
Old 04-15-2018, 10:28 PM
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You won't get any SRS information from a OBD2 code reader. The OBD2 interface is for engine only. You need a Mercedes-specific scanner that can talk to the airbag computer in the w210. In my '98 E300, I have to hook up via the 38 pin connector in the fuse box under the hood, I think all w210's are like this.

The SRS light will NOT reset itself, even if the problem is corrected! You must clear the error code from the airbag computer in order to clear the light. I discovered this myself when I replaced my steering wheel a while back - I had to insert the key and turn to "on" to rotate the wheel. The airbag was disconnected when I did this. When I put everything back together, the SRS light was on, where before it was not. I drove it like this for two weeks and the SRS light never went away. Finally I hooked up an MB diagnostic computer and cleared the code from the airbag computer, and it hasn't come back.

I would first read what the code is from the airbag computer, and make note of it. Then clear the code and see if it stays cleared. If it comes back immediately, you know the problem is legitimate and can begin troubleshooting from there.
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  #4  
Old 04-15-2018, 10:46 PM
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Most of the time it is the child seat sensor in the passenger front seat. Mine has the problem too.
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Old 04-16-2018, 07:33 AM
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All above is true
- SRS data does not come through the OBDII on a W210, it comes via the 38 pin and can only be cleared with HHT or Xentry
- If you take apart anything SRS related on the W210, be sure to disconnect the battery, or you will be setting codes that can’t be cleared with anything but a HHT or Xentry
- The seat recognition sensor is a common problem on these. You have to take the seat apart to repair it. Mine ended up being a broken wire in the harness from the sensor to the plug on the seat rail. They had zip tied the harness to the seat frame and it broke there. The wire was a low strand count so could not handle the flexing and movement. I grafted on a piece of cable that used to be a computer power cord (that has a high strand count) using solder and heat shrink tubing and it has worked great for about 3 years. When the seat sensor starts to fail you will see the “passenger airbag off” light coming on next to the window switches even though someone is sitting in the seat.
- Clock spring is another common failure point on these, this is easy to replace once the steering wheel is removed. Just be sure the wheels are pointed straight ahead when doing this.
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  #6  
Old 04-18-2018, 11:32 PM
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Quote:
Originally Posted by MB140300SD View Post
Most of the time it is the child seat sensor in the passenger front seat. Mine has the problem too.
Same with mine. There is a cheap part you can splice in to by-pass the child seat sensor. This fix will, however, keep your passenger airbag active even when there is no passenger in the seat. So if you get in an accident it will go off.
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  #7  
Old 04-19-2018, 12:21 AM
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Quote:
Originally Posted by MB140300SD View Post
Most of the time it is the child seat sensor in the passenger front seat. Mine has the problem too.
I agree that the seat sensor is a common problem. The seat sensor went bad on my car (a '98 E300 turbo diesel) several years ago. I bought a replacement from a dealer and was going to install it myself, using DIY instructions from Benz World posts. I took the car seat out and started as instructed. I seemed to me I was going to rip the seat upholstery and cause more problems than I started with so I sought help.

I called around and found a car upholstery shop that could do the job. They charged me $100 and did good work. That is a small fraction of what a dealer charges. I haven't had any problem with the light since then.

I didn't have the codes checked on my car, because the srs light did not come on all the time when there was someone in the passenger seat. When someone left the car (as when I dropped my wife off at work), the light came on when the seat was vacated. 'The was enough for me to figure the problem was the seat sensor.
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  #8  
Old 04-20-2018, 06:58 AM
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Fortunately the seat sensor does not set a latching code in the SRS controller. There will be history in Xentry (actually on a 210 it’s the HHT emulation application) of the sensor failure but it does not leave the light stuck on once it has been corrected.

I remember the seat being quite difficult to disassemble and reassemble, it was not a fun job.

Mine started showing the “airbag off” light even with someone in the seat and it progressed to showing the SRS light when the wire completely failed.

Fortunately it’s a 3 conductor cable from the seat sensor to the yellow plug in the seat rail, so a computer power cord with the ends cut off is a perfect candidate for a replacement cable. These are much more flexible than the cable originally supplied and the jacket is much tougher as well. A little solder and heat shrink and it’s better than new.

This is something you can check before ordering a new seat sensor. Run the seat all the way up and all the way forward then have a peek under the seat from the right rear passenger seat area. You will see a wire that goes from the seat rail terminal block that disappears into the middle of the seat cushion. They zip tied the wire to the seat frame. If you clip this zip tie you’ll see that the wire is probably severely kinked here. If so that’s likely your problem, and you can just disassemble the seat and fix the wire instead of ordering a new sensor.



Edit: Just thought of something. It may be worthwhile to just graft your replacement cable close to where the wire emerges from the seat cushion. Mine broke at the point a few inches down from where it emerges from the padding, where they had zip tied it to the frame. This would mean you would only have to pull the seat and flip it over to make this fix, instead of having to take the seat completely apart and pull the cushion apart.
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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older sonís DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Last edited by jay_bob; 04-20-2018 at 11:04 AM.
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  #9  
Old 06-19-2018, 10:16 PM
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I took the seat out today and disassembled it. It was actually not as hard as I thought, and no upholstery shop is needed. I went to a friends shop that has online auto repair data service (like alldata). He looked up the seat occupancy sensor, and printed out some information on how to test the system. I will be testing it in a couple days, and will post the results (I left the papers behind ). I have a parts car, and pulled the passenger seat and put it in my friends car so he can have passengers until I get the sensor sorted out. I did not notice any chafed wires, but I will find out for sure when I get back to it to test the system.
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'99 E300 W210 SRS light on-0619181611.jpg  
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  #10  
Old 06-20-2018, 02:39 PM
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Test info

Here are photos of the test info for the "passenger front seat occupied recognition sensor".
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'99 E300 W210 SRS light on-0620181128.jpg   '99 E300 W210 SRS light on-0620181128a.jpg  
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  #11  
Old 06-20-2018, 04:27 PM
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The problem I had was the black cable coming from the module (which is buried in the well in the fiber pad below the sensor grid).
At the point where it was zip tied to the frame, the wires had internally fatigued. Not easy to see from outside the black jacket but I had a hunch so I carefully sliced the jacket off and sure enough it had the classic fretting failure just like what happens on the door harnesses.

Rant: can they not get this right? I work in industrial controls, we actually have it specified in the UL/ANSI product standards for our work that if we have a wire crossing a flex point it has to be a high strand count wire...this is such a common problem with MBs and their low strand count wire. Sorry just a total pet peeve of mine.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older sonís DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
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