1996 c200 auto, ABS light question

[zeaphod]

My lovely C200 recently developed a permanent ABS warning light.
The light came on after stopping, i.e. without moving off. It is now a permanent feature.
I have checked the OVP output to the ABS control unit - 14.2v with the engine running.
Am I right in thinking that because the light comes on before the sensors are activated, then it is more likely to be the ABS control unit than a sensor? - or will a short circuit or open circuit sensor cause this too?
I have checked the physical condition of the front sensors and rings, all looks ok. I'm not too sure how to separate the front sensor plugs at the wheelarch - ping the wire clip off and pull hard?

 

[television]

It is more likely to be a sensor fault they are be far the most common. If a sensor is open circuit then the lamp will be on

 

[zeaphod]

ABS sensor fault? -

Thanks for the quick response Malcolm. I measured the resistance of the rear sensor at 180k ohms, which seems much higher than other mentions on this forum.

 

[zeaphod]

rear ABS sensor resistance

I see from a few other posts that the single rear sensor should read around 800 - 1000 ohms. Looks like a trip to the dealers tomorrow!

 

[television]

That is way over the top, I do not have the figure to hand, but as you say on here.

Did you have a real good connection when you did the test, and if that is the value then to all intents and purposes it is open circuit

 

[bigasotonuk]

Hi,
Have you got Euro car parts over in N.I.? As they will be cheaper than a main dealer, I believe you will need an ATE part, Euro car parts pt. no. 417 22 0500

 

[zeaphod]

ABS rear sensor removal

The new sensor was £66, not too bad. FYI the resistance of the new is 1008ohms.
I've spent the morning trying to remove the old sensor. 5mm allen key removes the clamp bolt, but the bugger refuses to come out more than 5mm. Time for a pint, more force will be applied this afternoon.

 

[zeaphod]

stuck rear sensor

applied more force, still stuck. hard to believe it's just the o ring holding it in.

 

[zeaphod]

still stuck

still stuck. after 25 years of working on cars, i'm baffled. turns by hand, but will not pull out. have i missed something?

 

[zeaphod]

nasty plastic

and whoever designed the plastic cover over the evaporative emissions control cylinder was an evil genius. almost impossible to get at the bolts. almost defeated, the remains of the existing sensor are offering little purchase for the vise grips. drill and lever?

 

[zeaphod]

the train is coming - light at the end of the tunnel

Illumination: 10mm socket on the end of extn bar removed the placcy cover.
The sensor is still stuck - moved out another few mm after an hour. The new exposed part is covered in corrosion, which makes me think that the metal end is rusted in the diff.
Any experience/ideas appreciated. I really don't want to disconnect the light for the MOT.
Wish I had a set of ramps and decent lighting. Ah well, off for the night.

 

[zeaphod]

rear diff sensor removal

Finally removed the rear sensor this afternoon, after days of working at it.
I ended up having to drill several holes deep into the old sensor and lever/pick bits out.
Right up to the last moment I thought it wasn't coming, then out it popped.
Be careful not to drill right through the sensor - you dont want any swarf round the reluctor ring in the diff.
Getting the drill at it involved dropping the fuel pump and removing the fuel pump support cradle - both came off easily (10mm nuts).

 

[television]

So sorry you have been working alone on this,,I can recall someone else having the same problems, congratulations any way

 

[zeaphod]

thanks

Thanks for that Malcolm.
A great feeling of satisfaction when the ABS light went off.
It did take a mile or so after re-fitting, something for anyone else to take note of. Just plugging the sensor into the loom will NOT extinguish the light.

P.S. Had the car up to my local MB specialist this afternoon - they agreed with me on the "fun" to be had with this job.