Brakes: Another ABS thread.....

[Luxobarge]

OK, so for quite a while now like some others on here I've been chasing an intermittent ABS light. Sometimes it will go for a week or two with no light, but it's gradually been getting worse and will do it every other journey now.

I've done all the usual things - had the unit out and done the re-soldering thing, replaced the front ABS reluctor rings etc. but it's still doing it, so recently I thought I really should apply some science to it and read the codes.

I bought an ELM327 OBD dongle (as advised by 4x4 - thanks mate) and downloaded the 850 OBDII app on my phone, and sure enough I can now read the ABS codes etc. The App isn't the most user-friendly thing to operate, but it does do the job. The text on the screen is tiny! By the way, anybody with a 96-2000 car who's having problems reading the codes I can recommend this device, it seems to have very wide functionality including SRS, service light etc., will capture and display live data, all the stuff you'd want, and it's cheap at £20 delivered, plus £1.69 for the app download. It's a tiny thing, and now lives in my centre console ready for instant use.

So I found that i'm consistently getting a pair of codes, always both at the same time, 313 and 314 - rear left and rear right ABS sensor open or short circuit. Clear the code and next time the light is on it's the same two codes.

Now I'm not buying that I have two faulty rear sensors that both fail at exactly the same time, I think it's far more likely that I still have an ABS module connection problem, quite likely still a bad solder joint problem. So, some questions:

1) Does anybody have a pin-out diagram of the main ABS module plug, or at least can tell me which pins the two rear sensors are concerned with? If I'm going to go back in there with a soldering iron I'd really like to know precisely which pins I should focus my attention on.

2) I've also heard tell of some earthing points that should be checked and cleaned on these - I know about the main battery earthing point of course, but are there others, and if so can you tell me where I would find them?

3) Any other ideas that might be consistent with these symptoms?

I've already replaced the electrical part of the ignition switch by the way, and it cured an occasional loss of some electrical circuits but made no difference to my ABS problem.

The conditions under which it puts the light on are pretty random, sometimes it's come on when the car is actually stationary, so even less likely to be an actual sensor.

Really appreciate any info on the above, this isn't a show-stopping fault (it's always behaved at MoT time) but I'd love to crack it once and for all, and also hopefully gain some additional experience for the forum.

Cheers all

[volvo2]

Not sure if this is what you are after, but this is the 1995 version:

https://www.volvoclub.org.uk/tech/se...ngDiagrams.pdf

and also here (for 1994 model), on page 128:

http://www.volvo850.ru/shem/1994.pdf

[Luxobarge]

Brilliant! Thanks Volvo2

Actually, searching around my PC I just found the 1997/1998 diagrams (my car is a 1997 V70, sorry, should have mentioned that) and I found the ABS wiring pages.

Seems like I've answered one of my questions, from the diagram it appears that the Left Rear sensor goes to pins 2 and 10, and the Right Rear sensor goes to pins 1 and 17.

Now the question is where are these pins on the plug/socket? Hopefully they'll be physically numbered on the socket, but I can't remember from last time I took it apart, so that'll have to wait until I can get in there, unless anyone knows?

Cheers

[Bob Meadows]

https://www.ebay.co.uk/itm/125378422912

Hi Luxobarge:~
Reading your thread with some interest, I also have a '97 V70 2.5 petrol.
Would you confirm that the attachment is the one that works for this model.
Thanks Bob.

[SteveSarre]

Hi Luxo

Just a thought. The two failures might not have happened at the same time.

Since you have only recently been able to read the codes, you might have had one rear sensor failure for a while, and then a further sensor rear failure.

So when you check now, you see two faults.


BTW as far as I remember, the rear ABS connectors live near to the top of the fuel pump (under the rear cargo floor).

Hope the Covid is better.

HTH
Steve

[Luxobarge]

Originally Posted by SteveSarre

Hi Luxo

Just a thought. The two failures might not have happened at the same time.

Thanks Steve, I know what you're saying and was aware of the potential for confusion when first doing a code scan. So therefore when I got the scanner working the first thing I did was clear all codes. I then ran the car to see what came back, and the first time the light came on I immediately scanned again, and the two codes were there. Cleared them again, and they've returned both together each time the light has come back on.

Covid much better thanks, feeling about 90% OK now. Cheers!

[Luxobarge]

Originally Posted by Bob Meadows

https://www.ebay.co.uk/itm/125378422912

Hi Luxobarge:~
Reading your thread with some interest, I also have a '97 V70 2.5 petrol.
Would you confirm that the attachment is the one that works for this model.
Thanks Bob.

Hi Bob, yes, that's the fella. Recommended by user 4x4, so I bought that specific one, as he (and others) say that apparently not all ELM327 dongles are the same, and some may have connectivity or other issues. I can't promise anything on anyone else's car, but I can confirm that it works on mine so I see no reason it wouldn't on yours. Cheers

[SteveSarre]

Hi Luxo

As far as I recall, one time I was working with a mechanic who had a more fully equipped garage than I do.

We had an ABS problem, and we connected up a meter/oscillosope to each ABS sensor in turn (the sensor was unplugged from the car harness, but sensor just was left in place in the wheel hub). Don't need ignition on or anything like that.

When we spun each wheel we could clearly see an oscillating signal. Good enough info to know which sensor was bad, and possibly to check that reluctor rings were in close enough contact.

HTH
Steve

[4x4]

From what I know the rear left ABS sensor is a default code and does not necessarily mean that there's a problem with it. So if it were my car I discount that one for now and check the rear right sensor along with the ABS unit and connections

[El Padrino]

Originally Posted by Luxobarge

I bought an ELM327 OBD dongle (as advised by 4x4 - thanks mate) and downloaded the 850 OBDII app on my phone, and sure enough I can now read the ABS codes etc. The App isn't the most user-friendly thing to operate, but it does do the job. The text on the screen is tiny! By the way, anybody with a 96-2000 car who's having problems reading the codes I can recommend this device, it seems to have very wide functionality including SRS, service light etc., will capture and display live data, all the stuff you'd want, and it's cheap at £20 delivered, plus £1.69 for the app download. It's a tiny thing, and now lives in my centre console ready for instant use.

Hi Luxobarge, glad to hear you're getting over the COVID. I had my ELM327 OBD dongle delivered, as advised by 4x4 and downloaded the 850 OBDII app. You're right about it not being the easiest to operate. I've not gone into any depth (due to time) but it did connect fine and I did a scan under the ABS sub-menu. The output I got wasn't what I was expecting. The codes came out in hex. Do they need to be translated to the Volvo DTCs via the jonesrh.info website? I was hoping it would do a scan and the fault codes would come up just like that. Obviously there's more to it than that upon first impressions. Will do another scan later for the ABS code information.