Abs

[studley07]

ABS light comes on dash, just randomly not on all the time. Done it twice now but just pull over switch off and start again light goes out and stays out. Relay maybe or could this be the start of something more sinister!

[Tractor Dave]

Might be a dirty ring or sensor. Have you checked for codes?

[studley07]

Thanks Dave. Not checked for Codes, wouldn't know how too. Car's a 1990 aqc 7a engine.

[Tractor Dave]

Ok, not sure if you can read codes on that early car. Have you got a black plug and a white plug on the side of the fuse box? You need an adapter (available on ebay) and a copy of VCDS (cheap version free from interweb) to read codes. If you are near West Wales I have full VCDS and can help.

[mdz]

There's no computer diagnostic option on abs under 1994. Only multimeter, oscylloscope and visual inspection.

[studley07]

Thanks for that. I am aware there is no obd port. All I wanted to know is if anyone else had come across this. This is why I don't do the forum anymore with smart answers like that. Never mind I'll sort it

[Tractor Dave]

I think he was just trying to be helpful.
You can buy a cheap oscilloscope these days and just connect up to each and sensor and check you have a nice wave.

[mdz]

Dave is right - I'm not trying to be a smartass, just wanted to save you some time looking for diagnostic tools that are no use in this case.
Usually dead sensors or broken wires triggers light/error instantly, broken rings after short distance of driving. Incorrect gap between sensor and ring or some rust on the ring usually makes abs to work at very low, nearly stopping speeds. Never heard of control unit going bad.
Since restart cures the problem, it might be sticky relay (there's 2 of them in abs unit and one somewhere else) or solenoid causing this.
These intermittent issues are pita to catch out especially in this case where are no "error memory" you can read. I'd wait and see if it gets worse and then make measurements according to wiring diagram - http://s2central.com/S2_Schematics/D/D26.pdf

[4WDrifter]

Might be a dirty ring or sensor. Have you checked for codes?

On an MB are the sensors simple enough normally to remove and clean? Or normally total PITA? Is there some sort of plastic cap/spacer on the end of them? Do the rings clean or does a blast of air do the trick/

[Tractor Dave]

Never worked on an MB but if they are the same as WR have a small plastic cap spacer on the end. Held in with one small nut. And yes, can be a pita to get out. Ring is hidden by bearing carrier on end of cv so very limited access without taking apart.

[4WDrifter]

Never worked on an MB but if they are the same as WR have a small plastic cap spacer on the end. Held in with one small nut. And yes, can be a pita to get out. Ring is hidden by bearing carrier on end of cv so very limited access without taking apart.

Thanks Dave for the guidance. I’ll see how I get on. There are a few second hand ones for sale on eBay so they must come out occasionally. Is there any way to test/check them when they are in?

[Tractor Dave]

Yes. Get yourself a cheap oscilliscope. Connect up to the plug and spin the wheel. You should see a constant regular wave.

[Robertbozic]

I think he was just trying to be helpful. Eldfall Chronicles
You can buy a cheap oscilloscope these days and https://piktid.com/ai-generative-face-fill/ just connect up to each and sensor and check you have a nice wave.

I appreciate the advice!