ABS TRACS lights coming on intermittently

[El Padrino]

Further update ....

I managed to get to the wire block connector and the smaller 2-pin power plug on the ABS module and cleaned the connectors and sockets they plug into with WD-40 contact cleaner. I left the piece of plastic wedged in. These are the results:

1. Upon turning on the ingnition, the TRACS light went out immediately but the ABS light stayed on.

2. Turned on the engine and the ABS light is staying on.

3. I went for a test drive and the speedo wasn't working. The ABS light stayed on throughout the one hour drive. The TRACS light never came on.

4. I tried turning off the TRACS via the dash button, but the TRACS light didn't come on. It would stay on until I took my finger off the TRACS button.

5. On the test drive, I didn't get the buzzing or vibrating sound from the brake pedal below 30MPH as I have been previously.

6. Switching off and on the engine hasn't made a diiference - the ABS light is still permanently on.

7. At home I connected my OBDII connector and did a scan with the Torque app with the ABS light on. The scan said no faults were found in the ECU.

I've taken out the piece of plastic wedging for now and will take her for another drive to see if the first issue of both ABS and TRACS come on and off intermittently again or if just the ABS stays on permanently. If the the ABS light still stays on permanently, I hope the indy's scanner will pick up a fault. I sense the ABS module could be faulty. I may have made things worse by cleaning the ABS module connectors

Luxobarge - many thanks for your replies with very helpful tips.

[Luxobarge]

You're welcome, I've had a lot of trouble over the past couple of years with intermittent ABS light on mine, which I THINK I've just fixed by replacing both ABS reluctor rings. My fault was intermittent though, sometimes it would do several journeys without fault..

OK, so the speedo is driven by the front left ABS sensor, so with no speedo this is a huge indicator as to where the problem is, it appears to be not getting a pulse from that sensor. In the absence of codes to confirm it, I'd say that's where your fault is. Personally I'd leave well alone at the module end, and have a look at the front left sensor, start by cleaning it and checking the reluctor ring very carefully (I'd recommend a bright light and magnifying glass) or possibly replacing that sensor to see if it cures the problem. It's still possible that the fault is at the module, but less likely.....

It's a shame you can't see the codes, there WILL be one there.

By the way, when you have an ABS light on, it's there because of a detected fault obviously, and will stay on for as long as the fault is there. However, if you fix the fault, or the faault disappears for some reason it will still show the fault light until the ABS has done a successful self test. This includes the car needing to be driven at above 15 mph, so you will always have the light stay on until you've exceeded 15mph, at which point if the module hasn't detected a fault it will put the light out.

[El Padrino]

Originally Posted by Luxobarge

You're welcome, I've had a lot of trouble over the past couple of years with intermittent ABS light on mine, which I THINK I've just fixed by replacing both ABS reluctor rings. My fault was intermittent though, sometimes it would do several journeys without fault..

OK, so the speedo is driven by the front left ABS sensor, so with no speedo this is a huge indicator as to where the problem is, it appears to be not getting a pulse from that sensor. In the absence of codes to confirm it, I'd say that's where your fault is. Personally I'd leave well alone at the module end, and have a look at the front left sensor, start by cleaning it and checking the reluctor ring very carefully (I'd recommend a bright light and magnifying glass) or possibly replacing that sensor to see if it cures the problem. It's still possible that the fault is at the module, but less likely.....

It's a shame you can't see the codes, there WILL be one there.

By the way, when you have an ABS light on, it's there because of a detected fault obviously, and will stay on for as long as the fault is there. However, if you fix the fault, or the faault disappears for some reason it will still show the fault light until the ABS has done a successful self test. This includes the car needing to be driven at above 15 mph, so you will always have the light stay on until you've exceeded 15mph, at which point if the module hasn't detected a fault it will put the light out.

Hi Luxobarge, it is shame I can't read any fault codes with my OBDII reader. Can you recommend one that won't cost hundreds of pounds that can read codes off a 1998 vintage? I'll have a go at cleaning the left ABS sensor first. It 'should' be fine as it is new and was only installed in July 2023. The front reluctor rings I've had checked and were reported fine. Are there any more differences between the left and right front ABS sensors, apart from the left one driving the speedo?

As someone who hasn't tinkered with cars much in the past, it's been interesting troubleshooting this issue and means I've got to know the car a bit a more Wish I had more time to do it. I thought getting a pre 2000 car would be simpler to maintain than the overly electronic modern cars, how wrong was I However, I do really like the car and plan to keep her going for as long as possible. This forum is a great resource for advice and tips from the likes of your good self and many others who contribute.

[Luxobarge]

Originally Posted by El Padrino

Hi Luxobarge, it is shame I can't read any fault codes with my OBDII reader. Can you recommend one that won't cost hundreds of pounds that can read codes off a 1998 vintage?

OK, so I'm not an expert on diagnostic systems for these cars, but I believe I'm right in saying that an ELM327 dongle (plugs into the OBDII socket and communicates via bluetooth) can be had for around £20, and then you'll need the Volvo 850 OBDII app for android phone - a couple of £ I believe.

Now this is interesting, as I too have a persistent intermittent ABS light, and having done all the obvious things I'm taking my own advice and finally getting the above dongle so that I can read the ABS codes too. Mine's a 1997 V70 T5, and like you I've found that my generic OBDII scanner is fine for engine codes, and possibly gearbox although I've never tried, but won't do ABS, SRS etc.

I've ordered it, and it should be with me in a couple of days, so when it arrives I'll have a go at downloading the app onto my phone and see if I can get it to work. Member 4x4 on here seems to know a lot about the various diagnostic tools available, so I'm following his guidance here, given to another member on another thread, where (with reference to the dongle) he says: This one will work https://www.ebay.co.uk/itm/125378422912

I wanted to follow his recommendation as apparently not all ELM327 dongles are the same, some work better than others it seems.

I'll let you know how I get on.

[Luxobarge]

Originally Posted by El Padrino

Hi Luxobarge, it is shame I can't read any fault codes with my OBDII reader. Can you recommend one that won't cost hundreds of pounds that can read codes off a 1998 vintage? I'll have a go at cleaning the left ABS sensor first. It 'should' be fine as it is new and was only installed in July 2023. The front reluctor rings I've had checked and were reported fine. Are there any more differences between the left and right front ABS sensors, apart from the left one driving the speedo?

OK, there's another thread on here about ABS light by Duke1 who said he'd put a new sensor in it. However, when he found that the code consistently pointed at that sensor, he had another look and found that being an aftermarket sensor it had a slightly different plastic moulding shape where it sits in the steering knuckle, something like an extra bit of plastic was protruding, and preventing the sensor from sitting down properly, so it didn't work. I think he removed/smoothed the extraneous bit of plastic so it sat in its mount properly and the ABS light went out and stayed out. If you've fitted a "new" sensor, worth checking this very thoroughly IMHO.

This is the thread from Duke1, well worth you having a read through this:
https://www.volvoforums.org.uk/showthread.php?t=335591

[El Padrino]

Originally Posted by Luxobarge

OK, there's another thread on here about ABS light by Duke1 who said he'd put a new sensor in it. However, when he found that the code consistently pointed at that sensor, he had another look and found that being an aftermarket sensor it had a slightly different plastic moulding shape where it sits in the steering knuckle, something like an extra bit of plastic was protruding, and preventing the sensor from sitting down properly, so it didn't work. I think he removed/smoothed the extraneous bit of plastic so it sat in its mount properly and the ABS light went out and stayed out. If you've fitted a "new" sensor, worth checking this very thoroughly IMHO.

This is the thread from Duke1, well worth you having a read through this:
https://www.volvoforums.org.uk/showthread.php?t=335591

Thanks Luxobarge, I read Duke1's post and it does sound similar to my issue in that we both have an aftermarket ATE ABS sensor. I guess the OEM ABS sensors are no longer available from Volvo

[El Padrino]

My car has passed her MOT for another year, so it's a sigh of relief. The ABS light has been coming on again intermittently, but miraculously stayed off during the MOT .... Phew!!! I thought the problem had been solved during December 2023, as she had both front ABS sensors, both the front wheel bearings and front reluctor rings replaced. My last scan with the 850 OBDII scanner pointed the issue to be the ABS module solder joints, but the indy's scanner said it was the n/s/f ABS sensor.

So, the next task is to re-solder the joints on the ABS module, as that is the only part that hasn't been looked into. I managed to remove the ABS module and open it up. The ABS module was rebuilt back in Jan 2023 and I can't really tell if the solder on the pins for the power and signal are cracked, dry etc. Now I'm in posession of a new soldering iron, I'm going to re-solder all the joints that cause the ABS/TRACS light to come on. For the solder joints/pins I've marked out in red, should the two be soldered together?

[Luxobarge]

Yes, as you can see they are soldered together and this is correct. They are the main power feeds for the module (which feeds the pump) which therefore carry a lot of current, so they share two pins each to share the load.

All the best, let us know how you get on.

[El Padrino]

Originally Posted by Luxobarge

Yes, as you can see they are soldered together and this is correct. They are the main power feeds for the module (which feeds the pump) which therefore carry a lot of current, so they share two pins each to share the load.

All the best, let us know how you get on.

Hi Luxobarge, as always thanks for your replies with the useful information. I'll be making a start on the soldering tomorrow. I've ordered a pot of flux too to help the solder, even though the solder I have already contains flux. I can't even remember what I last soldered or when and something I don't always do, so I'm just going to do it. This link (https://www.volvoforums.org.uk/showthread.php?t=72655) in the sticky by Jod T5 suggests re-soldering these pins in addition (see attached), so may do those too whilst I have the module open.

[Luxobarge]

Yes, those are the pins from the multiplug connector, and are usually the main culprits - they were on mine, under a magnifying glass I could clearly see the cracks in the solder around several of the pins.