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Photo DIY - SRS Seat Sensor replacement

363328 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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Can someone please fill me in about the type and quality of wire used to replace if that turns out to be the problem. I have no problem with doing the repair myself, as i have completely rewired classic cars in the past and consider myself fairly handy. However I would like to take the proper safety precautions with the wire that I use to replace this. Any advice will be appreciated.
Guys, I had to remove the side airbag from the door and I disconnected the yellow cable in the back. I plugged everything back on as it was but now I have the SRS light ON. I previously posted that I replaced the seat sensor 7months ago and before this side airbag removal the light was off. How can I fix this?

This is my understanding I have gained from tons of online research and dealing with SRS issues for the past year on my C320. Anyone feel free to correct me if im wrong:
Unlike seat sensor issues, the SRS light will not turn off on its own if there is a connection problem with the airbag. It sounds like may have tripped the code by unplugging the airbag either when the key was in the car, or battery was plugged in(I have yet to conclude which is standard procedure for dealing with SRS, some say just take the key out, some say unplug battery). In this case You just need to take the car to an Indy or the dealer, someone with the MB diagnostic system to turn the light off for you. In the case that you created an issue doing whatever it was you were doming in the door(loosened wiring, soldered joint, or connect)which it is quite possible that you did, You need to get that fixed. Once again someone with a diagnostic system can plug it into your car and both tell you what the issue is if there is one, or simply turn off the light for you. In my most recent case, the code was reading that the connection to the passenger side door airbag had a reisistance that was too hig(they called it "pass. side door airbag ignition squib" or something, ignition squib simply referring to the airbag device that explodes and make the airbag deploy) My fix was a bad connector in the wiring for the airbag in the step/sill of that side of the car, very close to where the door attaches and the wires go from the frame to the door. Its 2 wires, and the fix to just cut out the connector(used to detach wiring if the door ever needs to be removed, called "wiring disconnect") solder and seal the wires together. Then I went to an indy who has diagnostic system and they were able to turn it off. It was the third attempt at trying to turn it off after i was advised to fix three separate things, this one worked. Trial and error. Hope it helps
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