124 ASR fault

[tintinmt]

My 300TE 24v has some kind of ASR fault that has become gradually more frequent. The ASR light illuminates on the instrument panel and the throttle becomes virtually unresponsive. On several previous occasions I have simply switched off the ignition and re-started the car to clear the fault. However; lately, the fault has occurred frequently when the car has been left for a couple of days in the garage and is harder to clear by switching off the ignition. The car has a newish battery and the fault has not coincided with any recent work on the car. From a bit of internet study, I think I should be investigating the speed sensors that I understand are part of the system and maybe the associated wiring if I can identify it. I am trying to figure out the link between the fault and the car being left standing.
Does anyone have any helpful suggestions please?

 

[carat 3.6]

I'd read the flash codes before anything else.

 

[tintinmt]

Unfortunately, it seems that with this age of ASR (1990) there are no fault codes.

 

[bolide]

AFAIK the ABS only has one sensor on the rear (in the diff) on a W124 so the ASR has separate sensors. I know of a couple of cases where replacing the sensors has cured the problem

Nick Froome

 

[tintinmt]

I have followed the wiring from the connector (by the fuel pump) to the top of the diff. Unfortunately, it looks like considerable work just to get access to the top of the diff.

 

[carat 3.6]

Unfortunately, it seems that with this age of ASR (1990) there are no fault codes.

Have you got the 8 or 16 pin diagnostic socket?

 

[tintinmt]

16 Pin

 

[carat 3.6]

16 Pin

If you have a wire going up to pin 14, see what codes are active.

 

[tintinmt]

Hi, I read the codes. On PIN 14 (Engine Control I think) I got 2, 3 , 4, 6, 12, 13, 14 - Jeez!
On PIN 8 (Ignition) I got 17 which I read as Vehicle Speed Sensor.
I cleared the codes and reset the adaptation.
I took the car for a short run. I tried the kick-down which worked, but I did not try the cruise control. On return, the engine control codes remained clear but the Ignition showed code 17 again.

 

[carat 3.6]

Hi, I read the codes. On PIN 14 (Engine Control I think) I got 2, 3 , 4, 6, 12, 13, 14 - Jeez!
On PIN 8 (Ignition) I got 17 which I read as Vehicle Speed Sensor.
I cleared the codes and reset the adaptation.
I took the car for a short run. I tried the kick-down which worked, but I did not try the cruise control. On return, the engine control codes remained clear but the Ignition showed code 17 again.

That's alot of codes on pin 14.

Pin 3 gives you codes for the cis-e system
Pin 8 gives you ignition faults
pin 14 should cover asr

Pin 8 code 17 comes up as crank position sensor

Which codes do you have on pin 6?

 

[tintinmt]

I've not read PIN 6 as my notes don't cover it. I will check later. I took the cover off the ABS / ASR unit under the bonnet. I was unsure about the connector above the 2 relays in the image. Does it look to be in the 'locked' or closed position? It appears to slide left to right.
By the way - engine number is 104980.

 

[carat 3.6]

I've not read PIN 6 as my notes don't cover it. I will check later. I took the cover off the ABS / ASR unit under the bonnet. I was unsure about the connector above the 2 relays in the image. Does it look to be in the 'locked' or closed position? It appears to slide left to right.
By the way - engine number is 104980.

Cant help you with which way the slider goes to lock the plug in, asr on a w124 is such a rare uk option I have never needed to remove that plug.

.980 - the best engine you could have.:bannana:

 

[tintinmt]

I don't seem to get any codes on PIN 6 - just a solid light. Don't know if am doing something wrong. PIN 8 is still giving code 17.
Having read the owners manual for ASR; amongst other things, it says that the spare wheel and road wheels must have the same size tyre. I wonder if a flat or worn tyre could cause the system to show a fault?

 

[bolide]

Having read the owners manual for ASR; amongst other things, it says that the spare wheel and road wheels must have the same size tyre. I wonder if a flat or worn tyre could cause the system to show a fault?

The sensors detect differences in rotational speed between the wheels, so yes

Nick Froome

 

[tintinmt]

Since the ASR light has been known to not extinguish on start up, it seems unlikely to be caused by tyre differences, although it is plausible for the one or two instances where it has been known to come on whilst driving. I can't say that I have noticed any issues with the tyres, so I still favour the faulty sensor diagnosis. Logically, the system must perform some kind of check when the engine starts to check that the sensors are sending the expected status. If a fault is found in the ASR then the relevant instrument panel lights. In my experience this also causes the throttle to be inhibited.
Anyone have the work instruction for replacing the sensor on the diff? I can't imagine it's easy due to having to get access to the top of the diff.

 

[tintinmt]

Hi, I still have this fault and before taking it to my normal repairer I thought I'd try swapping out the sensor. However; as per my previous post, I can't see how to access the sensor as it is on the top of the diff. Any thoughts on how to gain access please? If I undo the prop shaft can I rotate the diff forwards?
If anyone has access to the work instruction I would appreciate a copy.

 

[carat 3.6]

The easiest thing to do is to remove the diff, 45mins will see it out.

 

[tintinmt]

I've got a nasty feeling that with my skills it will take a bit longer than that.

 

[hotrodder]

Destructions index Mercedes Benz Model 124 - M104 Maintenance Manuals 42-0820 covers rear axle ASR speed sensors along with some other ASR stuff. Section 30 also contains stuff on ASR

With regards to tyre size/circumference there must be some tolerance before the system gets confused*, dunno if ASR is fussier than ABS in that regard but FWIW i've had an 8 hole with 205/60r15 mixed with AMG ll and 225/45r17 on mine before due to a puncture. Initially one of each on the front and then a pair of 205/60r15 on the front for a few days until i got around to sorting the puncture. They differ by around 8mm in dia / 22mm in circumference and the ABS system didn't bat an eyelid
As you say i'd expect the warning light to go out initially and then come back on when the car moves if it wasn't happy with tyre sizes or some other mechanical problem that'd only be spotted by the leccy side when the car's moving

* cornering for example, the outside wheels are travelling along an arc with a radius ~ 1.5m bigger than the inside wheels

 

[tintinmt]

I agree that tyre size or inflation is very unlikely to be the cause but I confirmed that the tyres were correctly inflated anyway.
I'm sure the info I'm after is in there somewhere however, the more I read the more I thought I'd leave it to the experts. The manual seems to say that the rear axle assembly can be lowered slightly to allow access, but I don't understand the method.
As I say, I think I may have to hand the car over for a professional diagnosis rather than thinking about removing the diff to get at the sensor.
My normal place want the fault to be present in order to allow diagnosis. Unfortunately, when I drove it to them the fault disappeared on route.