124 ASR fault

[grober]

Havn't been following this thread and you really need to get those fault codes pinned down. http://www.diakom.ru/CARS2/pribor/cs1000/manual/cs1000_mb.pdf This is good on ASR 2 http://www.w124performance.com/service/w124CD2/Program/Chassis/42-0800.pdf
The first thing that leaped out was OVP =overvoltageprotection relay ----- these often go faulty resulting in odd faults. Frequently they can be repaired by resoldering dry joints on the small internal printed circuit board. The other "electrics " possibility is the electronic throttle pedal potentiometer- slider contacts of these can wear also. Lots of things on these analogue systems that can throw up warning light faults.

 

[tintinmt]

From my earlier adventures I think the diagnosis by code reader is limited. I will have a hunt around the OVP, brake light switch and throttle position switch looking for some thing obvious.

 

[bolide]

In my first post I said the ASR system has additional sensors - that's true of ASD, I don't know about ASR

ASR will work by comparing the rotational speeds of the two rear wheels. These will differ, as someone pointed out, when cornering, so the system may have a steering angle sensor like 4-Matic

If you can establish what sensors feed it, and what startup checks it performs, you may be able to pin the faulty down to one (or more) possibilities

If you take the diff out, replace the diff bushes while you are in there. If you drop the subframe, consider replacing the leading subframe bushes at the same time

Nick Froome

 

[bolide]

Have a look at this thread:
ASR fault on W124 M104890 - Page 3 - PeachParts Mercedes ShopForum

There's a chap trying to help but I suspect he thinks it's a late M104. So ignore all the early posts and look at page 3

Late M104s (2.8, 3.2) have a throttle body with a clutch mechanism for cruise control. Early ones, like yours, appear to have a mechanical actuator like the rest of the W124 range. It seems this is used by the ASR

Cruise on most W124s uses a Hall Effect sensor on the speedo to generate a speed pulse. I think the ASR system may use this as well

W124s have three ABS sensors, LF, RF and diff, so to operate any kind of ASR or ASD I would think they need additional sensors to compare rear wheel speeds

Does your car have an additional sphere for the ASR system?

Nick Froome

 

[tintinmt]

bolide, You are right that this is an early system. I have been given a paper on the way the system works but it's complex and the variations over time and model make it a mine field. I don't know if I have an additional sphere. Diagnosis seems difficult using codes - as there may not even be any for my car.
Whatever the fault, it is sensed immediately by the system and is not affecting ABS or cruise. I've checked OVP, brake switch and looked around for anything obvious.
My main thought is that it is the sensor on top of the diff as a failure here fits the bill - of course I could be completely wrong

 

[John Jones Jr]

My main thought is that it is the sensor on top of the diff as a failure here fits the bill - of course I could be completely wrong

Just a thought, doesn't the ABS use the diff sensor too? If so and the ABS is working I say it's fair to say the sensor is o.k..

 

[tintinmt]

Just been reading the ASR fault thread on Peachparts as in post 24. Symptoms sound identical. Solution seems to have been replacement ABS/ASR ECU.

 

[carat 3.6]

Just a thought, doesn't the ABS use the diff sensor too? If so and the ABS is working I say it's fair to say the sensor is o.k..

Your spot on there, the abs and asr do run off the same sensors.

 

[John Jones Jr]

Just been reading the ASR fault thread on Peachparts as in post 24. Symptoms sound identical. Solution seems to have been replacement ABS/ASR ECU.

Long shot. Take out the ECU, clean all the contacts and check the wiring loom for good measure - early W124 looms can degrade too. You never know.

 

[tintinmt]

I was thinking that the sensor on top of the diff was only for ASR. I will now pull out the ECU and see if I can see anything. I'll get a part number and see if any used examples are available.

 

[John Jones Jr]

I was thinking that the sensor on top of the diff was only for ASR. .

Early W124's (W201's also) had 3 channel ABS, thus three sensors - two for the front wheels one for the rear wheels.

 

[carat 3.6]

I was thinking that the sensor on top of the diff was only for ASR.

You should have a sensor above both diff output flanges, normal diff's just have one sensor on the diff input flange.

 

[tintinmt]

I'm pretty sure mine has more than one on the diff.

 

[tintinmt]

I think one on each side plus the one on top. (of diff)

 

[carat 3.6]

I think one on each side plus the one on top. (of diff)

There isn't one on the top, only above the output flanges.

 

[tintinmt]

Mine doesn't have one on the output flange......

 

[carat 3.6]

Mine doesn't have one on the output flange......

You should have a sensor where the yellow bungs are.

 

[tintinmt]

I have sensors where the yellow bungs are.
I can also see a cable running up to the top of the diff. 'Nothing on the output flange - it would be easy to check condition if it was there.

 

[carat 3.6]

I have sensors where the yellow bungs are.
I can also see a cable running up to the top of the diff. 'Nothing on the output flange - it would be easy to check condition if it was there.

The yellow bungs are above the output flanges, the cable you can see could be for one of the fuel pumps. There are no sensors mounted in the top of a w124 diff case, only 2 above the output flanges for asr, or 1 to the left of the input flange on a non asr diff.

 

[tintinmt]

Ah yes - mixing my outputs and inputs! Sorry! They are there on the outputs but nothing on input. Don't think I'm dreaming but I think I have seen MB schematics with sensor on top of diff?
I thought I'd followed the cable from the connector next to the fuel pump through the cable guide under the output shaft and up to the top of the diff. In the pic you can see the three cables and the fact that there is no sensor on the side of the input.