ABS problem

[Tunku]

Will big scrape marks in ABS sensors cause a problem picking up the signals from new reluctors? The deep scrapes came from the old reluctors rusting and snapping.

[Slade Alive]

Providing the body isn't damaged enough to prevent the coil from movement then no. The shape of the outer casing shouldn't have any bearing on the electro magnetic field created by the cutouts passing the coil. But then I'm not an electrician nor an expert in such matters.

[Rich_W]

Yes it will because the air gap won't be correct. So you'll get the ABS chuntering away for no reason as it's getting confused and thinking the wheel is not turning.

[rsv gone!]

I believe you can check by unplugging the sensor and turning the wheel. You should be able to measure an a/c voltage.

[seagrey]

rsv gone! said:

I believe you can check by unplugging the sensor and turning the wheel. You should be able to measure an a/c voltage.

Thats tricky without a decent multimeter,or a scope.
Better to test resistance,It helps if you know what the resistance should be but if you test all four then it wont matter.
Firstly connect a mutlimeter set to ohms across the terminals of each sensor,note the readiings with the wheel stationary.
Compare readings,if any are wildly different from the rest then its likely thats the culprit.
if not test again while rotating the wheel/hub you should get a fluctuating reading,not always smooth but it should fluctuate.hth.

[Jimmyarm]

You could just put it back together and see if the abs light comes on....

[Slade Alive]

Rich_W said:

Yes it will because the air gap won't be correct. So you'll get the ABS chuntering away for no reason as it's getting confused and thinking the wheel is not turning.

The air gap won't have been affected but it's nice to know someone will always come up with an alternative.

[Rich_W]

He did say "big scrapes" so it does rather depend on that. IME they tend to be a bit fragile if you wipe the end of them off.

HOWEVER. It matters not, because like so many technical questions on PH. The OP asks, there's a handful of answers (some better than others) and then that's it. The OP never updates the thread, or even acknowledges peoples input. So whats the ing point in trying to help?

[littleredrooster]

rsv gone! said:

I believe you can check by unplugging the sensor and turning the wheel. You should be able to measure an a/c voltage.

You will get a fluctuating voltage, but not AC as the magnet cannot rotate about its poles - (it's a crude square-wave).
Your voltage meter should flicker!

[Tunku]

Rich_W said:

He did say "big scrapes" so it does rather depend on that. IME they tend to be a bit fragile if you wipe the end of them off.

HOWEVER. It matters not, because like so many technical questions on PH. The OP asks, there's a handful of answers (some better than others) and then that's it. The OP never updates the thread, or even acknowledges peoples input. So whats the ing point in trying to help?

Ahem! How very dare you!!
Seriously, I've been on night shift, so incommunicado.
Today, a new sensor arrived in the post, so I can compare it to the existing ones. I would say that about 2 mm is ground off the end of one, not all over, but leaving a shoulder. The other one is not quite so bad, but definately grooved.
I will be replacing the right-hand one tomorrow, weather permitting,(snow is forecast FFS!).

Here follows a brief history of the abs problem -

Started as a low speed abs on, on a specific left hand downhill corner into a car park at less than 10mph. Abs engaged, no warning lights.
Got stuck in snow, lots of spinning and forward/reverse gear, abs lights on. Always cleared after fun and a restart. Did this a few times.
Snow melted and abs lit up for no reason. Would always reset.
Started to read about abs. Bought ELM327 OBD2 usb lead for laptop. Purchased TouchScan software to reset engine lights, reset codes etc. Fixed my old Mondeo problems with this.
Plugged into V70, P0500 code Vehicle Speed Sensor “A” problem.
Found out I could reset service light using trip meter, this gave me a “22” on the message centre. Looked up Volvo specific abs code in VADIS for 22. Gave me front offside speed sensor problem.
Put 2 and 2 together and looked at abs sensor and reluctor ring on front offside.
Reluctor ring was rusted badly and broken. Looked for reluctor ring replacement online and found one that might fit, but was not specifically for my car model. Bought one at £7.99 to check it would fit. It did, but needed to be cherry red with heat to go on CV joint.
Test drive put lights off briefly. Next day, abs light, brake warning light and engine light were on. Message centre said I would die soon if I kept driving. Put engine light out with laptop. Abs and brake lights stayed on. Lost speedometer and engine would cut out at every junction where no throttle input was needed to stop car.
Looked at nearside reluctor ring, It was broken and rusted too. Replaced it with same ring as right-hand side.
Test drive turned off red brake light warning. Only two orange lights now, engine light and abs light. Speedometer started working and car no longer cuts out.
Checked both sensors for wear and here we are. Abs light stays on permanently, but you can see by the low speed behaviour of the speedometer, that it is doing a check at 20 kph and failing. Engine light comes on if cleared and shows P0500.
It does seem to point to the abs sensor wear caused by the initial snapping of the rusty reluctor rings being the problem.

Edited by Tunku on Tuesday 8th March 20:33

[Tunku]

Quick reply to myself

Was cold and snowing this morning so put off going out to the car. Went out this afternoon.

The ABS is working, all lights out. Hurrah!

It was the more badly scraped one of the two front sensors, the right-hand one. I replaced it with a known working secondhand one.

[Slade Alive]

You should carefully hacksaw around the end of it taking the tip off. You might see where the damage has interfered with the coil - or not. It's all a learning curve! Thanks for the update too

[Tunku]

Slade Alive said:

You should carefully hacksaw around the end of it taking the tip off. You might see where the damage has interfered with the coil - or not. It's all a learning curve! Thanks for the update too

It still shows the same resistance as the replacement, just the end is curved. Maybe grind it flat to maintain the airgap?

[Slade Alive]

Was thinking along the lines of the damage being more than skin deep. I don't buy that air gap theory in the sense it's nothing more than scored.

[bunnysquasher]

I saw that you mentioned V70, not sure if it's relevant but a very common problem with these is that there are dry solder joints in the abs module. I'm not sure which ages of V70 share the same abs module but my 97 V70 is the same module as 850 described below.

I did the following fix on mine a year ago and it has been fine since.
http://www.matthewsvolvosite.com/forums/viewtopic....

[Tunku]

bunnysquasher said:

I saw that you mentioned V70, not sure if it's relevant but a very common problem with these is that there are dry solder joints in the abs module. I'm not sure which ages of V70 share the same abs module but my 97 V70 is the same module as 850 described below.

I did the following fix on mine a year ago and it has been fine since.
http://www.matthewsvolvosite.com/forums/viewtopic....

Mine is fixed. Not the module, just two reluctor rings and a front sensor (offside(UK)) Total cost £50.