ABS lights, no speedometer, HELP!

[C70InSuffolk]

My 2005 C70 has just one fault but it won't get through the MoT with it.

The ABS light has been on and off for 2 years. When it's on the engine management light is on as well. I did the diagnostics and replaced the nearside aBS sensor. That worked for a mile, then same again. Replaced the clutch sensor. 3 miles that time, then more Christmas tree on the dashboard effects. Replaced the brake pedal sensor, as that's what the diagnostics were saying now. Great. All back to normal. For at least 5 miles, then no speedo,. no trip kilometre, ABS light is on, engine management light is on. Then it's saying ABS sensor again.

Replaced it. Half a mile. Cleaned up the big wheel thing behind the disc brake. Great. 13 miles. Now the speedometer is out again, ABS light is on, engine management light is on BUT - switch off and everything looks fine. Switch on and for about ten seconds everything is as it should be.

Then before your very eyes, ABS light is back on, engine management light is back on, trip mileometer reverts to a line of dashes.

This is really seriously frustrating and obviously it isn't passing its MoT like this. Can anyone help before I scrap it? It's only just got 80,000 miles on it.

[SteveSarre]

Hi C70InSuffolk

What equipment are you using to do your diagnostics? Some readers might be more helpful than others.

ABS problems together with no Speedo is sometimes caused by a faulty ABS module.
Get the part number from the ABS pump unit. The ABS module lives just below that and will have a part number one number higher or one number lower lower than the pump unit (but I don't remember offhand which). The ABS module is held on by 4 small Torx 5 bolts. Dont try to remove those bolts with anything except a Torx 5 socket because there is a good risk of stripping them. You have to work by feel because the ABS module is out of sight below the ABS pump.

An oscilloscope can help you diagnose a faulty reluctor ring (the toothed ring at the outer end of the CV join on the axle).

The engine management light would usually be accompanied by a code which should tell you what the engine management problem is. I would guess that it is not related to the ABS problem.

But it is best not to guess!

I am not sure what you meant by "Cleaned up the big wheel thing behind the disc brake".

Hop that helps,
Steve

[Luxobarge]

In addition to the above, I'd be taking out the ABS module and re-soldering the pins where the multiplug goes on the PCB - a VERY common fault on these, your lack of speedo is almost certainly associated with your ABS problems and you've already replaced the sensor.

[C70InSuffolk]

Thanks - the big wheel thing is now known as the reluctor, so thanks for that. Now... where did I leave my oscilloscope last?

Where on earth am I going to find one of those!??

[Keith M]

Hi, I've got a 2003 C70 and a few years ago had the ABS warning light.
Replaced a sensor which had a worn tip and a broken reluctor wheel. Still had intermittent lights so used an Autel MD380 reader which gave me individual faults and a real time wheel speed when driving.
Swapped sensors over and eventually used a set of splitter cables that I made up to run both front inputs from one side which proved the system and narrowed it down to another reluctor wheel, which didn't look damaged but cured the problem once changed.
When I had faults on both front inputs the speedo disappeared as you described.
Hope this may help. Keith