ABS light on 1995 model

[jpliddy]

hi guys
are you familiar with ABS system on the 940 diesels light comes on when i switch ignition on and start car without moving and stays on volvo put these on later models as you know its a mot failure so hope its not terminal i don't want to go out and buy new sensors if its something big like the modulator or control unit
i did get a bit of a rattle noise a while ago on turning ignition on before starting i wonder if thats anything to do with my ABS can you give me any directions to go forward ?

[jpliddy]

hi
i have had the front wheels of and carefully cleaned the sensor and the cogged
o ring so no dust and metal particles are showing on sensors on front wheels
but i have not touched the rear wheels as im not sure what goes on with threat wheel set up , i have read some info from the Haynes manuel on the braking system but im struggling to sort this out
regards jim

[v8volvo]

If that light is on, it means the system has detected a fault and has a message waiting for you about what the fault is; all you have to do is ask for it. We need that clue in order to have a direction to go with our diagnostics. Here is the procedure for retrieving codes from the ABS self-diagnostic system.

http://www.swedishbricks.net/700900F...de%20Retrieval

Carry out this simple procedure from start to finish, write down the 3-digit code(s) that it gives you, then look up the code(s) in the fault table to see what they mean. Then report back here and we can advise on what to do about it based on what the actual specific issue is.

[jpliddy]

hi V8volvo
thanks for your valuable support on my problem ,
i have done what you asked and we have a fault reading 1-5-2.
so hopefully we have progress . right front wheel sensor ,open circuit ,or short -circuit battery to voltage.
can you advise me on what i should do next
im most grateful for your support
regards jim

[v8volvo]

Excellent, that is good news. Now you know exactly what type of problem to look for, and where to look for it.

A circuit fault is usually an easy problem to fix. This is most likely a problem with the wiring harness or with the sensor. I.e. a broken or shorted connection, either in the wiring to the sensor or in the sensor itself. Cleaning of the sensor or its tone ring won't help unfortunately, since the code reflects that the diagnostics found an issue with the actual electrical structure of the circuit, not with its performance or readings.

The theoretical next step for troubleshooting would be to test the wiring harness from the control unit to the wheel sensor for continuity and shorts. However, another option would be to just replace the sensor straight away. There is a pretty good (not guaranteed, but good) chance that that will fix the problem in this particular situation. And they are so cheap and easy to replace that you may as well begin there.

Here is a search on UK Ebay by the part number (Volvo P/N 3515092) that shows many results for around 20 GBP. https://www.ebay.co.uk/sch/i.html?_f...15092&_sacat=0

You could probably get one for very cheap from a breakers also. Or if you want to do more diagnostics before buying anything, you also could try swapping the sensors from the left front to the right front and vice versa, then check for codes again and see if it gives you a new code showing that the fault moved to the opposite side.

But simplest route, I would just give a new one a try and see if that solves it. You may also need to go through the procedure to erase the fault codes in the ABS computer after replacing the sensor to confirm that the fault has gone away and doesn't return.

Let us know how it goes!

[jpliddy]

hi V8volvo
thanks for your information on my ABS problem .i am thinking of doing what you suggest and replace the sensor .take it the right hand side must be drivers side over here England well i have loosened the allen key bolt which secures the sensor but the sensor will not move no way it seems like its glued into place ! but its never been off since new 25 years ago! so do you have any advice here ive read that someone had to break theres into little bits to free it of it must go through a locating hole in wheel housing i think .so just asking before i progress any further !
regards jim

[v8volvo]

Originally Posted by jpliddy

well i have loosened the allen key bolt which secures the sensor but the sensor will not move no way it seems like its glued into place ! but its never been off since new 25 years ago! so do you have any advice here ive read that someone had to break theres into little bits to free it of it must go through a locating hole in wheel housing i think

Yes you may have to destroy the sensor to remove it if it's corroded into the knuckle. That problem does commonly occur in "salt belt" cars here in the US and I believe road salt is used in many places in the UK too, right?

You could try spraying some penetrating oil on it and giving it a few days to soak in, that can only help, though sometimes not enough to make a real difference, but nothing to lose by trying it.

Yes you are correct, it goes through a hole in the knuckle and the other end then pokes out and sits close to the tone ring (some call it a "chopper wheel", it is a Hall effect signal generator) that is mounted to the wheel hub and read by the sensor. I can't remember how this all looks on a Volvo 7/9 series as I have not had this part of the car apart in many years on an ABS equipped model. Someone else may know better and be able to further clarify, or you may want to refer to a service manual which should show some pictures or diagrams. In general, on some vehicles you can get enough stuff out of the way to pound the sensor out from the other side, which can be a quick way to get rid of one that's stuck. But in some designs that approach is labor intensive, if for example it requires disassembling the front wheel bearing, front brake, etc. Take a look at it and you will probably be able to see what needs to be done.

But easiest outcome would be if you can get some penetrant to free up that sensor and twist it out from the back side with some pliers, where no other parts of the car will need to come off for access.