SRS light behavior - PeachParts Mercedes-Benz Forum

tbomachines · #1 07-03-2010, 04:24 PM

My SRS light has been going on and off recently. Usually it will only stay on for a few seconds. What other systems is the SRS light tied to (research indicates maybe voltage regulator??)?

- no ABS or CEL on at all, except normally at startup
- SRS light likes to come on more when ambient temperature is really hot (90+ makes it occur more often)
- ONLY comes on at a stop or coasting, as soon as the car starts moving (even rolling after a stop) the light goes out
- car seems to be running fine, hard cold starts but that is likely due to a small small fuel leak after I changed the filter and didn't tighten everything up (on the top of the to-do list)
- There is NO correlation to steering wheel position and the light being on, so contacts are probably out of the equation.
- Does not matter if there is a passenger or not, still comes on regardless

It seems to be happening more regularly now, especially since it is hot out and I want to make sure it isn't a major issue and/or a safety hazard. Any thoughts? Where can I start diagnosing the SRS system??

Jer · #2 07-03-2010, 07:11 PM

The SRS unit has fault diagnosis and will store codes in memory for you to retrieve later, as long as the SRS light is still on. You will need to make an impulse counter like the one in the attached picture. Attach the yellow wire banana plug to pin 6 of the X92 diagnostic socket on the firewall near the battery and the black banana to pin 1. Attach the red clip to the battery positive. Press and hold the button for 2-4 seconds and count the number of blinks. Do it again until all codes have been displayed. Tell us what you find.

tbomachines · #3 07-03-2010, 08:29 PM

Quote:

Originally Posted by Jer

The SRS unit has fault diagnosis and will store codes in memory for you to retrieve later, as long as the SRS light is still on..

It goes off after a few seconds.

tbomachines · #4 07-04-2010, 12:01 AM

Need to make an edit: It came on this evening as I was going up a hill, so not just while coasting or stopped, but it definitly occurs much more often when coasting or stopped. And Jer, thanks for the diagram I'm gonna have to solder one of those up.

tbomachines · #5 07-09-2010, 03:31 PM

Seemed to come on a bit more today, 93*F ambient temperature, no AC on. I'm stumped, hopefully will get to making a LED blinktester this weekend.

MBeige · #6 07-09-2010, 04:09 PM

My 190E and my uncle's 190E does the same thing. Thought it was the OVP relay (after reading some threads linking the OVP to the SRS light) but I don't want to replace items unnecessarily.

Hmm...

Pavka007 · #7 07-09-2010, 04:16 PM

I will make a wild guest here but if you are talking about your 300E perhaps I can point you into the right direction.

On the rear drive shaft (both sides) close to the tire side there is a RELUCTOR ring. The purpose of it is to read the magnetic field. You can buy them aftermarket. Mercedes will tell you that you need the whole drive shaft, YOU DON'T. You can fix this yourself inside 75 minutes, I've done it on W124.

The wheel sensor works by detecting a change in a magnetic field as a tooth passes it. This is seen by it as a pulse in the signal that it produces.

The Reluctor rings with the holes on are an aftermarket item designed to fool the sensor. The holes are aligned to fit over the gap between the teeth. It is the teeth rusting away that causes the problem. As a tooth rusts away the change in the magnetic field as it passes the sensor reduces and the pulse becomes less.

As there is more metal around each hole the sensor detects a change in the magnetic field similar to a tooth passing and a pulse is generated.

Perhaps you have notice that I am talking about TOOTH and RINGS, the reason is simple, original Mercedes shaft is with teeth and the ring is looking like bracelet with holes.
A lot of W210 back in the UK have this problem because of the rain and salt on the road and they have all the lights on

BAS, ABS, SRS as soon as the ring or rings are replaced everything is as good as new

I am sure that someone here in the US make them, but when I had to deal with it I've contacted a company in the UK and everything was done inside 4 days.
Have a look for yourself and check your rings. If you need someone to buy them for you from the UK and forward them to your address let me know I will help you with that if the company say that they can't post overseas. Just one more piece of info, all of the E-Class are the same size, so u can order any of them, it doesn't matter. I will ask a friend back in the UK, he was telling me few weeks back that he replaced one of them but he got 2 rings, so if he still have the second one, you can have it. for cost price plus shipping.

Good luck

MBeige · #8 07-09-2010, 04:20 PM

It seems it's occuring whether or not the vehicle is in motion (both in my case and the OP's case).

Pavka007 · #9 07-09-2010, 04:27 PM

Quote:

Originally Posted by MBeige

It seems it's occuring whether or not the vehicle is in motion (both in my case and the OP's case).

Yep...as soon as you turn the key the signal is alive, but once again...what model are we talking about here? I don't know about W123, I am talking W124. Just to be clear

tbomachines · #10 07-09-2010, 10:41 PM

I don't see how that would trip ONLY the SRS light though, if anything it would be the ABS light.

Pavka007 · #11 07-10-2010, 12:27 AM

I was just trying to help by offering different point of view. When i was dealing with this issue on my old W124 there was not ABS light on.
Good luck sorting it out.

sjh · #12 12-08-2010, 03:15 PM

Quote:

Originally Posted by Pavka007

I will make a wild guest here but if you are talking about your 300E perhaps I can point you into the right direction.

On the rear drive shaft (both sides) close to the tire side there is a RELUCTOR ring. The purpose of it is to read the magnetic field. You can buy them aftermarket. Mercedes will tell you that you need the whole drive shaft, YOU DON'T. You can fix this yourself inside 75 minutes, I've done it on W124.

The wheel sensor works by detecting a change in a magnetic field as a tooth passes it. This is seen by it as a pulse in the signal that it produces.

The Reluctor rings with the holes on are an aftermarket item designed to fool the sensor. The holes are aligned to fit over the gap between the teeth. It is the teeth rusting away that causes the problem. As a tooth rusts away the change in the magnetic field as it passes the sensor reduces and the pulse becomes less.

As there is more metal around each hole the sensor detects a change in the magnetic field similar to a tooth passing and a pulse is generated.

Perhaps you have notice that I am talking about TOOTH and RINGS, the reason is simple, original Mercedes shaft is with teeth and the ring is looking like bracelet with holes.
A lot of W210 back in the UK have this problem because of the rain and salt on the road and they have all the lights on

BAS, ABS, SRS as soon as the ring or rings are replaced everything is as good as new

I am sure that someone here in the US make them, but when I had to deal with it I've contacted a company in the UK and everything was done inside 4 days.
Have a look for yourself and check your rings. If you need someone to buy them for you from the UK and forward them to your address let me know I will help you with that if the company say that they can't post overseas. Just one more piece of info, all of the E-Class are the same size, so u can order any of them, it doesn't matter. I will ask a friend back in the UK, he was telling me few weeks back that he replaced one of them but he got 2 rings, so if he still have the second one, you can have it. for cost price plus shipping.

Good luck

I appreciate your comments and suggestions.