Brakes: 850: ABS light

[volvo2]

1994 Volvo 850 Petrol non-turbo

My ABS light came on after traveling about 50 miles. Did not come on again after switching engine off, restarting and driving another 50 miles. There is no issue with the ABS activating incorrectly when braking and I could her the ABS do the usual automated check at ~20 MPH

Would I be right in thinking this is unlikely to be a broken reluctor ring as that would most likely give a permanent issue?

[DaveNP]

In my experience, a broken reluctor ring doesn't come and go, an intermittent problem like that sounds a lot like the 'dry joints' problem in the ABS module on top of the ABS Pump, there's quite a few threads on here about that.
Your post makes it look like this is the first time it has happened so first off I would leave it to see if it repeats and how often. If it does come and go over the next few weeks you might want to try the bodge that I tried of wedging something like a folded bit of paper between the body of the ABS Module and the Plug, this pushes the plug fractionally to one side and keeps all of the joints in contact, if that stops the light coming on then I'd say it's certainly dry joints.

[amazondean]

Another trick that i tried and worked for a while, is to actually heat up those two pins with a soldering iron for a few minutes. The heat goes down the pins and if you are lucky, can warm the solder enough to make a better contact! It is often those two contacts that is the problem!

[Jod T5]

Originally Posted by volvo2

1994 Volvo 850 Petrol non-turbo

My ABS light came on after traveling about 50 miles. Did not come on again after switching engine off, restarting and driving another 50 miles. There is no issue with the ABS activating incorrectly when braking and I could her the ABS do the usual automated check at ~20 MPH

Would I be right in thinking this is unlikely to be a broken reluctor ring as that would most likely give a permanent issue?

This is a perfect example of dry solder joints in the ABS ECU, it will get worse and may improve with a wiggle of the two wire plug to the ABS Unit.
Resoldering the unit is not difficult, I regulally used to resolder these and Jaguar XJ units, gotta love Teves.


https://www.volvoforums.org.uk/showthread.php?t=72655



Cheers,




Jod


EDIT - If you are having issues with your headlights as well you may want to replace the electrical portion of the ignition barrel.


https://www.volvoforums.org.uk/showthread.php?t=54629

[volvo2]

Thanks. My ABS light has not come back on over the last 120 miles. I am a little confused though as I can't see the wire connections that you mention. Were there different ABS control units fitted? I have a 1994, 10 valve engine. My ABS ECU is a metal bodied plug unit, like the one shown in the attached image (not my car).

[JohnM 855 T5R]

Originally Posted by volvo2

Thanks. My ABS light has not come back on over the last 120 miles. I am a little confused though as I can't see the wire connections that you mention. Were there different ABS control units fitted? I have a 1994, 10 valve engine. My ABS ECU is a metal bodied plug unit, like the one shown in the attached image (not my car).

The 850 ABS units didn't suffer as frequently from dry soldered joints like the V70's.

I suggest two things. Disconnect the multipin plug and clean the pins with switch cleaner and a scrub with a nylon brush. Also, check the earth strap at the back of the engine is tight and making good contact. Both can cause intermittent ABS lights to come up. This fixed the problem with mine.

Regards
John

[DaveNP]

Originally Posted by volvo2

Thanks. My ABS light has not come back on over the last 120 miles.

I'd be inclined to leave it alone, if for no other reason than chasing intermittent faults is almost impossible.

I am a little confused though as I can't see the wire connections that you mention. Were there different ABS control units fitted? I have a 1994, 10 valve engine. My ABS ECU is a metal bodied plug unit, like the one shown in the attached image (not my car).

Sorry for the confusion, I leapt to the ABS plug like on a V70 without noticing we were talking about an 850 which your photo shows is different, the V70 is like this photo

the plug is towards the bottom right of the photo, the bit of red card is enough to push the plug sideways in it's socket and help it make contact.
It looks to me like the 850 plug is a much better system and more secure, JohnM's suggestions would seem a better approach.

[volvo2]

Covered another 120 miles with no ABS light...

[volvo2]

Just for information - the light never came back on (now several hundred miles later). It seems this earlier ABS unit does not suffer from the connection problem of the later model (contrary to what "850 Robert" seemed to be saying in one of his YouTube videos - normally helpful but on this occasion slightly confusing).

[amazondean]

The later 850 has the same set up as the V70. Well my TDI's do anyway!