Brakes: ABS/TRACS Fault

[richmac]

Hi Steve,

My V70 is almost full OBD2 but not quite so I stil have to manually input the model and year, so yes. Watching the ACC data, it looks as though there are vertical accelerometers in the wheel sensors but this is my guess and could be utter nonsense. My absent reading came back luckily.

For anyone who might be interested, I managed to clear all faults today although I suspect it's only temporarily. Cleaning the sensor and spraying contact cleaner into the main module plug did nothing. What cleared it, weirdly, was doing a series of lock-up breaking from about 20mph. The fault initially came on whilst holding stationary on the brakes so I suspect the ABS unit is probably the culprit.

Further info for anyone contemplating a 'quick' wheel sensor change. On my average condition car, they are apparently now a part of the knuckle as 21/2 hours of effort will testify to. I believe the only way to get mine out will to disassemble the front suspension and use a big hammer from below!

BR,

Rich.

[SteveSarre]

Hi rich

OK sounds like progress.

Yes getting those sensors out without breaking them can be tricky!

Steve

[richmac]

As expected, the lights and 443 code returned today, again whilst holding the car on the brakes, so the ABS unit is going for diagnosis and repair.

[SteveSarre]

Hi Richmac,

To remove the ABS module, make sure you use the correct Torx socket
E5

Anything else risks stripping the head and then that is a problem.

https://www.amazon.co.uk/sourcingmap.../dp/B07BQTKZQ9

Use WD40 etc to lubricate and wash the grit out of the connector shroud, and work back and forth until it comes up. Hopefully that way you won't snap anything.

HTH
Steve

[richmac]

Thanks again Steve. The way it's failing and other symptoms leads me to sending the whole unit away, module, valve body and pump, to be safe so at least I avoid the soft torx screws. The price is the same.

BR,

Rich.

[SteveSarre]

Hi Richmac

I wonder what they do with the pump? Do they test that too? Presumably you'll have to bleed the brake system afterwards. Are your bleed screws OK? You can buy new ones cheap and this would a good time to do it. Replace brake hoses too?

This cannot be to a cheap "resolder the joints" place. Let us know how it goes (and who it goes to).

Getting the module bolts off is fine if you use the right socket, and press upwards while you are cracking it loose. Inspect the bolts to make sure they have good heads before you put it all back together.

HTH
Steve

[ITSv40]

Originally Posted by SteveSarre

Hi Richmac

I wonder what they do with the pump? Do they test that too? Presumably you'll have to bleed the brake system afterwards. Are your bleed screws OK? You can buy new ones cheap and this would a good time to do it. Replace brake hoses too?

This cannot be to a cheap "resolder the joints" place. Let us know how it goes (and who it goes to).

Getting the module bolts off is fine if you use the right socket, and press upwards while you are cracking it loose. Inspect the bolts to make sure they have good heads before you put it all back together.

HTH
Steve

All sound advice. When bleeding the system, do use a pressure bleeder - I find the Sealey one very good. The ABS unit has many fine passageways in it and only a pressure bleeder will get all the air out. When I have let air into the ABS module I bleed the brakes in the normal way and then go round again and draw 250ml from each wheel to make doubly sure. May be overkill, but it makes me feel better.

[richmac]

Thanks both. I'll let you know how it goes.

[volvo again]

Buy good quality bleed nipples, I bought cheapies and couldn't get a firm pedal, found out that the bleed screws were sucking in air via the threads, replaced with good ones and no further trouble

[richmac]

A quick sweep up, fingers crossed, for interest.

Bottom line, this seems to have been caused, as suggested, by one of the power pins for the pump in the Control unit. The solder looked perfect but had seperated fractionally at the base from the board. Re-soldering the 2 pins seems to have fixed it.

I ended up fixing it myself so some personal observations:

The unit had clearly been opened and re-soldered before and very well so it was very difficult to spot the fault. the pins were all secure and the solder all looked in good condition. I have no multi-meter skills sadly.
Soldering is not easy no matter how it may look in the instructional videos even with steady hands and perfect vision!
Getting the unit on and off, however, is very straight forward and can be done without removing anything else, (turbo car).
After re-fitting, it took a few short driving cycles and full start/stops for the system to reset itself and come back to life - it seemed to need to do this rather than be OBD reset.

As an aside for anyone considering it, I also tried to do a master cylinder refurb shortly beforehand as mine is on the way out and I thought it might be causing the issue. Getting the unit in and out is really easy. However, if you have the original ATE version, the pistons are held in by a very strong eyeless circlip which neither my local garage nor I could remove. My only way forward, is , therefore, a new master as I don't fancy cutting it out!

I hope some of this is helpful for others with similar issues.

Rich.