Brakes: ABS/TRACS Fault

[richmac]

Hi,

Does anyone have experience/ knowledge of the following, please?

97/98 V70 2.5T

ABS + TRACS lights on with Code 443, which won't clear. Live data also indicates no signal from the front left accelerometer. All other readings normal.
The wiring and insulation all look in good condition.
Brake are otherwise fine although I was starting to suspect an internal MC leak due to slightly changng pedal pressure/position. I've bled the ABS but it was fine.

1. Where is the accelerometer?
2. Anything else I can check before I remove the whole unit and send it off to an expert.

BR,

Rich.

[Luxobarge]

"Accelerometer" is almost certainly another (confusing) word for the ABS sensor. I'd suspect your fault is either that sensor has gone faulty or it's the usual dry solder joints in the ABS ECU itself - both are pretty easy to rectify yourself, in the case of re-soldering the ECU it's a pretty much free fix too. Extremely unlikely that the ECU has gone faulty for any other reason, they're very reliable apart from the bad solder joints, which is a very common fault on these, especially on V70 models.

[volvo again]

As Luxobarge says, plus it may be worth checking the reluctor ring(s)

[SteveSarre]

Hi Richmac,

The 2 reluctor rings are the toothed metal rings on the fat part of the CV joints. They sometime get so rusted or scraped or cracked that they don't trigger the ABS sensor (which sits in the wheel spindle just below the front shock). Have a look at your reluctor rings.

The reluctor rings are cheap, but to replace it you have to disconnect the CV from the hub, remove the old ring and then sweat (heat) the new ring on. Almost easier sometimes to replace the whole CV joint (after market joints are cheap and will include a new reluctor ring).

The ABS sensor also sometimes fails. it is held in by a 10mm bolt, but the sensor is in a plastic housing which sometimes get well stuck in its hole, so be gentle if you pull it out.

Not sure how much a new sensor costs, but worth finding out.

HTH
Steve

[SteveSarre]

Hi Richmac

Skandix don't ship to UK but they are a useful source of information


https://www.skandix.de/en/spare-part...-axle/1010522/

Your ABS sensor Volvo part number is probably 6849311


Steve

[richmac]

Thanks Steve. My rings are all good thankfully and I'm getting strong, equal readings from my sensors in the 'normal' channels. It's the acceleromter feed that's missing from the front left so I'm trying to figure out where the module gets this signal from - ABS sensor or something like a yaw sensor. I'll give the ABS sensor a good clean anyway and see what happens.

[richmac]

Thanks. Are the P1 V70 ABS sensors multi-channel? I have good live data signals from the speed and wheel channels. The P2 V70s seem to have sensors under the seats as well.

[RollOn]

Re: Luxobargethe: "usual dry solder joints in the ABS ECU" - Yes!!
ABS Module/Control Unit: 4 years ago I re-soldered the 2 big/main posts (to power connector). This immediately fixed the ABS fault. This week, I again received multiple fault codes for open circuit wheel sensors and ABS pump fault. So, I wasted much time swapping wheel sensors without luck. Initially, I was convinced that the ABS Module/Control Unit (ECU) was no longer the problem. As a last resort, I properly de-soldered and then re-soldered all the smaller solder joints (inside the ABS control module). This again immediately removed all ABS fault codes.
Note: Dry joints (solder) only occur where the pins (for external wiring harness) are connected to the circuit board. (no other part of the board has problems) Every Volvo of this model has/will eventually have this ABS problem. Caused by faulty manufacture, “Made in Philippines”. Do not waste time on anything else until you have properly repaired the ABS ECU. (If properly de-soldered and re-soldered it should never again cause problems).
See Tutorial: https://www.matthewsvolvosite.com/fo...f6426ea4060a29

[Luxobarge]

As above. I re-soldered mine, and the fault disappeared for a few weeks. Then it came back, and was worse than ever. I delved around down by the plug again, and re-seated the little two-wire plug that carries the power to the ABS ECU, it seemed a little loose and not fully "home". Not a single problem since, and that was months ago.

Just thought I'd mention it, because a bad contact on this plug will give very similar symptoms to a dry solder joint, and it's very frustrating to get the problem back when you've gone to all the trouble of doing the soldering job!