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Photo DIY - SRS Seat Sensor replacement

362992 Views 157 Replies 78 Participants Last post by  caleno69
Your SRS light has come on and stays on, Also you noticed that the airbag off light stays on as well. Your car has never been in an accident, and your bags and belts have never deployed. You have some basic mechanical aptitude and don’t want to pay a dealer 500-800 $US for this repair. Read On…
It is not necessary but best to look for an independent mechanic shop that displays the 'pie', and have the codes read, this will tell you exactly what the problem is. Most will not charge for this service, and unless you have the MB software and can read the exact pin, you can’t do it..

Lets try and address the most common questions regarding this condition.

Q; - Is this a safety issue, the car still runs and a friend of mine who has a 2000 210 has a piece of electrical tape over the light and just drives it. Do the air bags still work?

A; No, Operation of all SRS devices are unpredictable, they may not fire at all, or they may fire for no reason

Q; How many Sensors are there and where are they?

A; Many.. The SRS system has a pre-tensioner in each seat belt, several air bags, sensors throughout the car to activate same, and a child sensor in the front passenger seat.

Q; Before I tear my car apart I would like to know as much as I can, what the module looks like and yhe functionality and design information

A; The child sensor adjusts air bag and seat belt level for the front passenger, and effects the functionality of several other devices.

Q; Is a sensor of some kind in the drivers seat?

A: No, a seat belt switch, and seat belt tensioner , and air bags.

Q; If I replace the Ass Mass will the light go off?

A; BE Clear Here, when you fix the fault, The Light WILL go off by itself if all faults have been corrected.

Q; How do I do this repair myself?

A; On the next posts, you will see a series of pics, but the procedure is,,,
1. At some point, have the codes read, by an inde, (PIC 1 ) as having the seat pad SRS light on will 'MASK' other ( emergency tensioning retractor belt and bag) faults.
2. Buy a NEW sensor first, (PIC 2 ) I have not seen ANY signs of wear ( wires, scraping, breaks ) at all. The sensor 'dots' fail with use/age. Sensors cost 140 US$ at MB.
3. TIP- Take the seat out of the car, period. If you have never done one, and are not an MB tech, or leather repair expert, 5 bolts and some clips and the seat is out. Don't even try to in car cover remove. you will me$$ it up!
4. TIP- Allow an extra 2 hours to shampoo the carpet under BOTH front seats. which is what you will do when you see all the gack under the seat. My car gets 'mini detailed' weekly and it still had lots of filth under the seat(s). Record amount of coins found so far.. $16.83 US$’
5. Unplug all wires from the connector block (PIC 6-7 )
6. Snap off the bolt covers (PIC 8 )
7. Remove all four 'Torx' type bolts (PIC 9-10 )that secure seat rails in place on the car floor.
8. Pull OUT not up on seat belt bolt cover(PIC 11 ) and remove bolt.
9. Release the wire cable (PIC 12 )
10. Tip the seat top down and remove the complete car seat from the car.
11. Remove the connector block and unplug the yellow sensor (PIC 13 ) connector from it's housing under the seat.
12.Take off the plastic side covers.
13. Loosen the 2 back bolts, (PIC 14-15 ) and remove the 2 front ones, This is optional and done to make the job easier.
14. Push down on the leather, (PIC 16-17 ) and pull out the bar that holds it to the frame.
15. Twist 90 degrees on the plastic ‘butterfly’ clips, (PIC 18-19-20 ) and release the leather cover.
16. Change out the sensor pad (PIC 21-22-23 ).
17. Once you have removed the sensor pad unit replacement is simply a reverse procedure. (PIC 24-25-26 )


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Use a multi-meter first

Hey all,

First off thanks for this great thread.

Before you go out and buy the sensor just try and check the condition of the lead 3 wire from the sensor. I removed the front part of the seat cover but left the back still on - while I tested. My brown wire had a fault and it was in a tricky spot. Past where the zip tie that lashes the wire to the seat frame - but just before the hole in the seat mesh / seat bottom. From the naked eye it looked fine - but it had broken - so test. I know I almost gave up but thought as long as I am in here.

I used a razor blade to carefully cut away the protective sheathing that covers all three wires and then used the blade again to carefully expose a small amount of wire to check for any loss in continuity. First I checked the white and it was fine then brown and it was the culprit.

Some tight spot soldering but in the end that did the trick and the light is off. There is no resetting or doing anything else - all good now. Ohh I did put protective tape on the metal hole where the line was cut and also put some sheathing on the brown and then the 3 wire.

It took me an hour and a half and I would not consider myself a mechanic - fairly handy with some tools but that's it.


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2005 c230 Kompressor:

I've got the SRS light and took it to the dealer. Codes came back saying that the child safety sensor in the passenger seat and the steering column harness were faulty. They want to charge me $1800 to repair them.

I believe I can do it myself and then have the codes reset, but I don't know the part numbers. Does anyone happen to know them or where I can find them?

I don't know the part number but the dealership would (I know thanks buddy - but it is a dealer only part I am sure). However in my case when I looked into it it the sensor pad was around $500. I would take the time first and check the wires - in my case they looked fine but when I did a simple test to see if the was a fault in the section of wire from before and after where the wiring gets pinched - a wire that looked fine was actually broken inside the sheathing. You can test this will a volt/ohm meter you get from Radio Shack - or an electrical store. This was in my E320 but in my C230 I have had that code go off when someone had been in the passenger seat and did not clip in their seat belt.

It looks a bit daunting to fix yourself - but really it is not that bad. If you are a bit handy with a soldering gun and have a few hours you can do it yourself - just go slow and I always use my phone to take pictures when I disassemble so that when things go back in I remember how it went.

Good luck
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I used 18 gauge wiring and that seemed fine - I would not be too concerned about it because it is not taking any load and considering as it started to break the wire it was getting thinner and thinner until it broke on the last strand.
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