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Photo DIY - SRS Seat Sensor replacement

362879 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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where to get the new sensor pad

Hi All,

A great thread that has been a great help and made it easy to get the seat disassembled.

Only problem i have is where to get a new occupancy sensor pad. Our local ones here do not have any in stock and the best price so far is $450.

If you can point me to a website or email address of a good supplier you would make me a very happy man.

PS I have a 2001 ML270 CDI (VIN: WDC1631132x746981)

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I have air bladders in the seats - does anyone know how this affects the replacement process?
Check the wires first

My SRS and passenger seat airbag lights came on a few days ago so I followed the excellent instructions in this thread to remove the sensor pad. Before assuming the pad was faulty I thought it was worth the time to inspect the wires.

Visually the wires looked fine, no chaffing or cuts in the insulation. I stripped off the outer insulation to reveal the 3 individual wires which also looked fine. As a final check I stripped back the insulation on each wire close the "box" and checked continuity from that point to the yellow plug. Sure enough, one wire was broken inside the insulation even with no sign of damage from the outside.

When my ohm meter showed no resistance on the white wire I lightly pulled on it from each end and it snapped in half. A quick splice and all is fine. The best part is it cost me nothing but a few hours of time.

If I had to do it again I would test the wires before separating the seat pad (white plastic clips) as the hardest part of the job was getting those clips to catch on the wires sewn inside the seat.

I hope this helps someone avoid the expense of replacing a perfectly good sensor.
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Does anyone know where to get the sensor for the $100 quoted. Multiple people have asked the same question but no one has stated where the sensors can be purchased this cheaply.

I got mine secondhand for £30 from the uk. Hopefully it was from a sales rep's car, not a family car! The one I put in has been in a family car with young kids bouncing on it for a year and no problems yet.
It is quick to change so I recokoned it was worth the gamble.
Good luck!
I chickened out

So far I have gotten the diagnostics, yes I need to fix it.
I went to a local upholsterer who has the Benz symbol on his card.
He offered to do the work for $20 hour. I get the pad.
At that point I froze.
As long as this is my work Benz (outside sales) I aint going to mess with it.
Maybe when I retire, joke.
Anyone want to reinvigorate me?

Much obliged,

Jeffinski Max
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Go for it....

Pulling the seat out is 4 bolts and a few plugs. If your slow, fifteen minutes. A qualified person could replace that sensor in less than an hour so why not go for it? Personally I would check the wires as that is the only thing that was wrong with mine and easily spliced. I could do the entire thing again in an hour without any skills as an upholsterer.

Don't let it scare you, the worse you can do is get it apart and need someone else to put it back together which still reduces the time you pay for. This is not rocket science. I would say a 3 on a scale of 1-10.
12279 hits and counting, oh my god...........

I had no idea this would go this far, thanks again greg and lord and all those who helped.

Let me see, 12279 at 1200 means that we have saved members $ 147,348,000 from the full dealer repair price.

MB must hate me.

OBTW- Hello from Stuttgart.

Question for all of you who have done the DIY and to MRBSMITH. My Passenger airbag light light goes on after start up but goes away. So, Is my passenger seat sensor working ok?. Do I assume that it is my driver seat sensor that is causing the problem and has anybody replaced or fixed the wiring of their driver seat sensor. MY SRS dash lights is currently on.

Any input would be great.

airbag light

The light should come on when the ignition is first turned on. This is a indication that the bulb is functional and the airbag and sensor are functional. If the light does not come on momentarily or if it stays on, then you have a problem. What you describes sounds normal

John May
2001 E55
seat pad sensor

BTW There is not a sensor in the drivers seat since it is not needed. If your dash SRS light "STAYS ON" then it is the passenger seat

John May
Has anyone done this on an SL r129 model? My srs code is that pesky passenger seat and I'm gonna tackle it but not sure of the removal process, are the bolts in the rails and 4 in rear with 2 in front? ...
to remove the r129 passenger seat cushion the entire seat does NOT have to come out, just the seat cushion ..... there are 2 bolts on the front of the seat horizonally ..... unbolt with 10m socket and seat pad comes up exposing electronics underneath .... be careful for at the rear of the cushion is the cable from the sensor that extends to the rear of the seat where it connects to the plug .... you may have to remove the rear plastic to get to the plug, its two phillip screws at the fold of the seat ....
I just tried this on my 99 E320 and the sensor looks like its brand new. I've checked continuity from the yellow plug to the box and all is well. I guess I'm the anomaly who's going to have to bite the bullet for the new pad.

Well... I ended up installing the pad back into the car because I didn't know when I'd get around to purchasing a new one and the light is gone. It would come on immediately 5 seconds of starting the car but just went on a 30 minute ride and nothing *fingers crossed*.

Kruso.... Make sure when you check continuity that you bend the wires across the entire length. A small break could make contact at sometimes and no others. To me it sounds like you just have a loose/broken wire or contact.
Kruso.... Make sure when you check continuity that you bend the wires across the entire length. A small break could make contact at sometimes and no others. To me it sounds like you just have a loose/broken wire or contact.
Good call :)... I kind of thought that and attempted to stretch out the wires as I was checking for continuity. I didn't think about bending it... if the light shows up again I might just replace all three of the wires altogether before forking over the bucks for the new pad.
Sorry to hear you need the pad...

Also, I have helped on 8 of these now, and I now solder the connections when replacing the wire.
Also, Also, Do Not.... try the incar pad replace if you keep your car in mint condition as most our members do, You WILL scratch somthing and then you will see that scratch every time you get in the car.
The audience here is first time novice DIYers, and with our wisdom and guidance they do quite well.

If anyone can post-up how to get into the multi-contour seats ( I need to replace the seat cushion and the length adjuster bladder) and provide the part No's for the bladder and cushion, I will buy a Premium Membership. :thumbsup:
Bladder A 210 910 03 75
cushion A 210 910 31 50
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