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Photo DIY - SRS Seat Sensor replacement

363182 Views 157 Replies 78 Participants Last post by  caleno69
3
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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Just replaced the pad for my neighbor car and it worked great. Thanks guys. Great thread.
Glad we could help

has it really been ten years???
omg.........
has it really been ten years???
omg.........
I got my first w210 320 and have this problem.....GREAT POST!:cool::cool:
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.
Thanks
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.
Most Any High Quality Wire..

will do the job.
To date, I have been unable to find a strap wire that is an exact replacement.
I do repair these now, and that is working well.
do solder the connections and carefully insulate ( shrink ) them.

So happy we could help.
B
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?

Thanks.
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?

Thanks.
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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Yet another happy customer

May the Gods of Shade Tree Mechanics bless and keep you.:wink

It has been over 50 years since I had a seat out, and there was no electronics then. I was apprehensive, but I am retired and just cannot afford MB's labor rates. The detailed instructions and pictures made this doable.

I was having an intermittent problem with the SRS lamp so I was sure there was a broken wire - someplace.

It took a while to get the seat out and exposed on a bench but it went well from there. I stripped the insulation of the 3 wire connector close to the end back at the seat. I then used a multimeter with a sewing common pin as a probe to poke through each wire's insulation doing a continuity test from there to the plug. All was OK until I pulled on each wire. The brown lead came out. Fortunately, the break was far enough out from the seat that I could splice it. A bit of Bench Tech work - stripping, soldering, shrink tube and it was done. SRS lamp now functions properly.

The break was right where the cable was tightly tie-wrapped to a passthrough on the seat steelworks. Definitely poor Manufacturing Engineering, the cable should have been able to flex freely. Note, this was a 2001 and the wires were stranded, not solid core.

Once again, Benzworld forum has saved me money.

Thanks,

Dave
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May the Gods of Shade Tree Mechanics bless and keep you.:wink

It has been over 50 years since I had a seat out, and there was no electronics then. I was apprehensive, but I am retired and just cannot afford MB's labor rates. The detailed instructions and pictures made this doable.

I was having an intermittent problem with the SRS lamp so I was sure there was a broken wire - someplace.

It took a while to get the seat out and exposed on a bench but it went well from there. I stripped the insulation of the 3 wire connector close to the end back at the seat. I then used a multimeter with a sewing common pin as a probe to poke through each wire's insulation doing a continuity test from there to the plug. All was OK until I pulled on each wire. The brown lead came out. Fortunately, the break was far enough out from the seat that I could splice it. A bit of Bench Tech work - stripping, soldering, shrink tube and it was done. SRS lamp now functions properly.

The break was right where the cable was tightly tie-wrapped to a passthrough on the seat steelworks. Definitely poor Manufacturing Engineering, the cable should have been able to flex freely. Note, this was a 2001 and the wires were stranded, not solid core.

Once again, Benzworld forum has saved me money.

Thanks,

Dave

Good Job, I had to buy the cushion :)
Just want to confirm that the cheap (< US$10) seat sensor on ebay such as this one works just fine:

Seat Occupancy Sensor Emulator Suitable for MB TYPE6 W220 W210 W203 W168 W163 OG | eBay

I just cut the wire from the original seat sensor and soldered the replacement sensor box to the yellow connector and zip tied the box the the seat frame, no more SRS light.

The emulator did ship from China and takes 1~2 weeks to get here, but for the price I'm ok with that.

Thanks for all the useful information in this thread.
2
GREAT THREAD!!! Thanks. Used it a lot this week when I replaced the seat bottom cover of my drivers side. Couple of things I want to mention while they are fresh in my mind. Take some photos or take some notes while you are taking things apart. I eventually got it all figured out I think, but it would have helped to have documented some things like the exact wire routing, how the seat back attaches to the seat bottom, etc. Most of it seems and looks obvious, but it all wasn't. I also had to borrow a T8 Torx for one tiny screw holding a cover on an electrical box. Never knew they came that small. My smallest one was a T10.

I took my time over a three day period, couple of hours a a day. Toughest part as others have mentioned was getting those little white clips to snap onto the wire. The new seat cover did not come with the wire BTW, so you have to reuse the old one.

All in all a very satisfying job and I'd rate it as a 7 out of 10 in difficulty. I'd much rather remove the intake manifold and change my glow plugs, but I'd rather do the seat rather than having to drill out a glow plug again. :)

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And it goes on and on...

I am so proud of all of you who have used this post to fix this common error.
DIY on....

B
I like this thread. My airbag light stays on (with passenger), but do not have the SRS light on (will have to check that SRS light works on key setting #2 ). My initial problem (just purchased my 99 E300D with 187k miles) was head rest does not work. I can solder and have multimeter, so good to go. Thanks.

P.S. SRS light works, but is not on after starting. Just no airbag light (by shifter) stays on (passenger or not).
2nd time in is a winner!!

I went into my seat again after the last failed attempt at fixing. I tried before stripping the wire cover at the bend under the seat, but my needle probe showed OK.

This time I took the seat cover off. Lot of work and probing to understand how the plastic wire grabbers/keepers come off the bottom of the seat cover. Little work getting them back on also.

After removal of seat sensor, I found an OPEN on the white wire at the module. Stripped the cover off farther along at the bend where I had stopped before and bingo, the wire was creased by the ziptie at the bend. Stripped and soldered wire together and put shrinkwrap on the wire before soldering. Taped up, checked continuity, all OK.

Thanks for this thread, really fixed a safety item.
I just finished replacing the seat sensor in my 97 E320 per the excellent information posted. I first checked continuity in the wires and was disappointed to find that they were intact...no breaks in the wires. I removed the sensor from the seat with no issues thanks to the play by play pictorial. I did a resistance check on the removed sensor and voila, there were two "dots" that were out of commission. An on-line dealer parts source sent me a replacement sensor mat for $133 including shipping. I replaced the mat, put everything back together and voila, the SRS light is still on. I live in rural PA where most people other than those who own a recently drilled gas well commonly avoid Mercedes Benz since the dealers are only located in the larger metro areas. Anyway, I guess I am going to have to get it scanned to figure it out from here. Thanks for the great info on this site.
W 204 c 180 , model 2008.
Message is appearing " F L Malfunc."
What is the issue
Can someone come up with a test procedure for wires?
Opening Seat Sensor Box

Great thread. I got my seat out of the car today. Made the mistake of using the MB workshop instructions, which were clear as mud. Wish I checked the forum first.

Anyway, I figure I'll replace all three wires because if one wire broke, the others probably aren't far behind. Therefore, I'm going to eliminate all traces of the original solid wire completely, from the connector to the black box on the sensor. So I'm trying very carefully to open up that box, but it doesn't want to cooperate.

Does anyone have a technique, short of breaking the plastic clips?

BTW, it's starting to look to me that broken wires may be common in other systems as well. My climate control wasn't working (blew hot except when on LO). Another thread directed me to the thermistor in the overhead console. Sure enough, one of the leads was broken. In fact, the leads were so brittle and fragile, they kept breaking with even the slightest touch. MB must have gone out of its way to find the one 10k thermistor with the thinnest, most fragile, bare copper leads. Tinned or covered leads would have made all the difference without affecting the unit's accuracy one iota.

Thanks in advance.
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Add me to the list of 'broken wire, but fixed' folks. The ground (brown) wire was broken on my seat sensor. I used this DIY and the WIS (for torques, 35Nm seatbelt bolt, 50Nm for the seat bolts).

One thing to note, my sensor is original with 174k miles on it. It just gave up the ghost one day. I managed to acquire a used sensor for a few bucks and found it was broken in the exact same place. The ground (brown) wire was shorted about 5 inches from the sensor control box.

Makes me wonder how many seat sensors have been thrown away due to a piece of wire...
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