How to resolve SRS warning light fault (W208)

[jamesmc]

I carried this repair out on my 1999 CLK230K (W208) Cabriolet however the solution/technique will no doubt apply to other MB models.

Problem:
1. SRS warning light on dash coming on intermittently or permanently
2. SRS warning light on console, between front seats, illuminated intermittently or permanently.

First thing to check:
As mentioned elsewhere in this Forum the light can illuminate when the SRS seat pad sensor connector under the passenger seat is suspect.
Disconnect, clean, reconnect, then check the connector for good continuity and re-check your SRS warning lights to see if they now stay off during normal use.

Next option:
If, after trying the above, the SRS light stays on then the most likely cause will be failure of the SRS sensor pad itself which is fitted into the front passenger seat base.

Replacing the sensor pad falls easily into the realms of a DIY repair.
The above image gives you an idea of what is already installed in the seat.​

Procedure for repair - I removed the seat to do this.

1. Unplug all connectors from under the passenger seat so that no wiring is left attached to the car.
2. Remove all four 'Torx' type bolts that secure seat rails in place on the car floor.
3. Remove the complete car seat from the car and place it upside down on a soft surface (eg: cloth covered table top)
4. Remove the yellow sensor connector from it's housing under the seat. I had to remove the housing (two screws) to release the connector.
5. Before releasing the seat cover you may wish to remove the plastic side covers from the seat.
6. Release the seat covering from around the frame (front and sides only - no need to remove completely) at the base of the seat.
7. Once the cover has been released turn the seat onto it's back.
8. Lift up the seat cover (front) and expose the seat pad sensor pocket.
   
   
   
   
   
9. Locate the white plastic box attached to the sensor pad.
   
   
   

   
   
   

   
   
   
10. Ease out the white plastic box and the sensor itself plus guide out the cable with the yellow connector from underneath, through the seat padding.
11. Once you have removed the sensor pad unit replacement is simply a reverse procedure.

Tip:
I actually fed the sensor pad into it's new home by hand but, if you look at the first image of the new pad, you will see that it's not a flat sheet and there is room for error when installing the sensor matrix into the seat.
It occurred to me afterwards (isn't hind site a great thing!) that I could have cut the cardboard (that the new unit was supplied in) and sandwich the matrix (sensor pad) in between two sheets of card.. feed the lot into the pocket and slide the sheets out afterwards leaving the matrix (sensor pad) behind.
Final adjustments can be made by hand afterwards.

After installation the SRS light issue went away permanently.

 

[jamesmc]

Has this post been edited by admin? I added images at relevant points in the post but they no longer show in the post itself. This kind of makes the post look a bit odd now with gaps etc.

 

[Blobcat]

Has this post been edited by admin? I added images at relevant points in the post but they no longer show in the post itself. This kind of makes the post look a bit odd now with gaps etc.

I can see pictures . I will copy this into the DIY section.

 

[star]

Good result, did you have the sytem checked before repair or did you carry out repair on a hunch,

 

[jamesmc]

The fault was there from when I bought the car from it's previous owner. Then it was intermittent. Later it converted to a permanent fault.

Just after I took the car on I put it into my MB dealer and had them perform a major service and got them to change out the ATF also so that I had a base to start from with the whole car. I asked them to let me know what might need fixing ASAP. There wasn't anything major (which was reassuring) but they flagged the seatpad sensor as being at fault. Until I checked the connector for continuity, I couldn't be sure.
I tested the connector with a multimeter and it was good, so I ordered the sensor pad and changed it anyway.

The car is a 99 and from what I have seen in the Forums this seems to crop up every now and then in slightly older cars, so it was worth a shot.

I seem to recollect that the part cost around Euro €90.00 (approx £65.00) but as I am offshore at the moment I can't check that.

 

[dragon]

Is there one on my 1997 W202?

 

[television]

Yes you do have a complete SRS sytem, that consits of the air bags and seats and belts

 

[dragon]

Yes you do have a complete SRS sytem, that consits of the air bags and seats and belts

I meant under the passenger or driver seat?

 

[television]

I meant under the passenger or driver seat?

Yes the simple test is to let someone sit in the passenger seat without doing up their seat belt,, if the warning comes up, then you have it, only when driving or engine running

 

[dragon]

Yes the simple test is to let someone sit in the passenger seat without doing up their seat belt,, if the warning comes up, then you have it, only when driving or engine running

Never bother to look underneath the passenger seat, can't tuck my head underneath it.

 

[Aussie Nick]

congratulations. Great thread, a real asset to the forum.

 

[lt4vette]

I have this exact problem with my 2000 clk320, so thanks to Jamesmc for the detailed instructions. My car has the air adjustable seats (with air bladders) and the dealer tells me this makes for much more labour time - has anyone performed this task with the air bladder seats, and if so, any additional hints?

 

[television]

I have this exact problem with my 2000 clk320, so thanks to Jamesmc for the detailed instructions. My car has the air adjustable seats (with air bladders) and the dealer tells me this makes for much more labour time - has anyone performed this task with the air bladder seats, and if so, any additional hints?

This does not add anything much to the time as the single pipe for the seats is just unplugged from the control switch, the pneumatic part is only on the back rest and not on the squab, so its the same as the above

 

[c220joe]

mine is W202 C220 1996 has srs warning light intermittently.
Actually, when turn the key on, SRS light stays 6 seconds and goes off for about 1 seconds then on again. And it lasts about 2 mins then off.
I'm thinking about how to check tyhe sensor under passenger seat, but wondering if it like W208 as procedure above. And is the pad part the same?
Anyone knows? Please give me a clue.
Thanks in advance

 

[ulik]

srs warning light wont go off

I had to replace a barrel lock on the driver side and had to take the airbag off I have since replaced and checked all connections put everything back and the srs warning light wont go off, I have just rechecked all connection in the door behind the panel and all looks ok can anyone help
Ulik

 

[Alex Crow]

hello. it would help if you at least tell us what car this is!!!!!! presumably a mercedes?

you probably just need the fault codes erasing, especially if the ignition was turned on AT ANY TIME that the airbag was disconnected.

 

[shayes]

On a current thread I've been looking to replace my seat squab but need to remove the seat heater and put it into the doner seat squab.

Your thread is excellent photographically.

Can you however tell me how you took off, (back) the seat cover as I can't figure this out.

I've added a photo and my only theory is that the three nylon clips if pinched will slide back through the Coconut matting and perhaps release the cover tension?

did you do the work while in situ on the frame as your photo's suggest?

Mny thanks

(oh also my sensor does stay on rather a long time but perhaps the doner squab has a better sensor.

 

[Cheshire]

"I tested the connector with a multimeter and it was good, so I ordered the sensor pad and changed it anyway."

Can you please explain how you tested the pad sensor? i.e what voltages, voltage drop etc to look for, resistance/continuity

I have SRS issues and trying to diagnose whether its the actual sensors in the pad or just the wires.

 

[rodisi]

"I tested the connector with a multimeter and it was good, so I ordered the sensor pad and changed it anyway."
Can you please explain how you tested the pad sensor? i.e what voltages, voltage drop etc to look for, resistance/continuity
I have SRS issues and trying to diagnose whether its the actual sensors in the pad or just the wires.

Good question.

 

[rodisi]

I don't know if this has been mentioned before but according to a friend Mercedes mechanic, the problem with the weight sensor in the passenger seat is usually caused by a high pressure on one spot as for example kneeling on the seat, like when trying to reach over to something. I know I've done that before.

In my case, the light only comes on when there is no passenger so if I want to get rid of the light, apparently there are connectors that are wired in a way to fool the system. When I do find one, I'll just have to make sure no children sit in the front.