ABS Experts in here please - Light on, 10.15v on one sensor lead, 10.85v on other.

[DMGRS]

Originally Posted by SD1too

Yes, but you'll need to rotate the road wheel in order for the square wave to be produced (see photo in post 11). Of course your multimeter cannot read a square wave. The display will appear to give random and quickly changing readings, so if you see this the chances are that your sensor is o.k., but it's a very unscientific test. An oscilloscope is needed to evaluate the output properly.

Simon

I'll try that, however if you have a look at the picture posted above there shouldn't be 10.xx volts on the wire in any circumstance - only between 0.6 and 1.2 or 12v, depending on which wire you test.

Going to grab a cheap ABS pump I found and a sensor, total of about £31.

[SD1too]

Originally Posted by mattyprice4004

... if you have a look at the picture posted above there shouldn't be 10.xx volts on the wire in any circumstance - only between 0.6 and 1.2 or 12v, depending on which wire you test.

Those voltages are with the wheel rotating. When you obtained 10 volts you admitted that you didn't turn the wheel, so forget about the 10 volts; it's meaningless!

Simon

[DMGRS]

Originally Posted by SD1too

Those voltages are with the wheel rotating. When you obtained 10 volts you admitted that you didn't turn the wheel, so forget about the 10 volts; it's meaningless!

Simon

OK, so with the wheel turning if I don't get 12v on one wire and a fluctuating voltage between 0.6 and 2v on the other, something needs replacing?

[SD1too]

I haven't seen any official voltage figures. Those quoted in this thread seem to have come from the anonymous website quoted in post number 9. I have no idea whether they are reliable or not.

As I've already explained, I doubt that you'll see a readable voltage of between 0.6 and 2 displayed on your multimeter because it won't be able to resolve the high frequency square wave.

As your speedo isn't working it's very possible that the OSF sensor is faulty. Unfortunately the only way to be sure is to renew it. That would seem to be the cheapest and easiest way forward.

Simon

[Greeners]

I'm assuming that the voltage will change from when the key is first turned, as the ECU does its check, sees the fault then will disable the sytem until the ignition is turned off and on again. (But I might be wrong !!!)

[carlpenn]

Originally Posted by mattyprice4004

Hi guys,

Got a bit of a problem with the 75 I've got as a project - I can't get the ABS light to work and the speedo doesn't function.

I've done the following:
- Battery reset
- Checked the voltages going to the sensor as per test procedure (measure voltage between ground and either wire) and after they sit at 10.15v and 10.85v respectively. From what I read, on a healthy sensor this should be 12v and between 0.6 and 1.2v.

The previous owner did say he had a replacement ABS unit fitted by his son and 'wasn't sure if it was the right one' (?!)

Where would you even start with something like this?

If I got a 2nd hand ABS unit, are they specific to the diesel / petrol models and do they need coding?

Cheers
Mat

There are 3 Types of ABS Unit.

Petrol and Diesel Without Traction
Petrol With Traction
Diesel With Traction

All 3 have different Markings. The markings are MK / ML and MN off the top of my head.

So first things first.

Petrol? Diesel? Traction or not?

MK is without Traction on all Models.
MN is Diesel with Traction
ML is Petrol with Traction

ABS Units are Plug and Play but you MUST have the correct Unit for your car

The Marking I speak of is at the top right of the Unit, so looking down at it, it will be nearest the front of the Car in the croner so to speak. Have a look at Rimmers Site, then you will see what I mean as they have Photos of each corresponding ABS Unit with correct Marking

[FrenchMike]

Originally Posted by SD1too

I haven't seen any official voltage figures. Those quoted in this thread seem to have come from the anonymous website quoted in post number 9. I have no idea whether they are reliable or not.

As I've already explained, I doubt that you'll see a readable voltage of between 0.6 and 2 displayed on your multimeter because it won't be able to resolve the high frequency square wave.

As your speedo isn't working it's very possible that the OSF sensor is faulty. Unfortunately the only way to be sure is to renew it. That would seem to be the cheapest and easiest way forward.

Simon

Simon, do the test yourself ! IT WORKS .

To me , 10 volts mean an open circuit inside the sensor simply ...

[Greeners]

Have you checked the co diction if the multi pin connector on the ABS unit


Not uncommon to fill up with water and corrode

[Mike Noc]

Originally Posted by SD1too

As your speedo isn't working it's very possible that the OSF sensor is faulty. Unfortunately the only way to be sure is to renew it. That would seem to be the cheapest and easiest way forward.

Simon

If you get an old ABS plug and socket from the scrappy Simon you can fit an extended cable between the two and plug any sensor into the OSF, which will prove the fault isn't on the speedo and test the other wheel sensor signals.

I made one up a year or two ago along with a brake pad wear indicator plug with the contacts shorted to quickly isolate a pad sensor fault.

[SD1too]

Originally Posted by FrenchMike

I don't know how it works ...

That's what you said earlier and I applaud you for saying so, because neither do I. What we are seeing in this thread is a lot of stabbing in the dark. We do not have details of the circuit within the ABS module. We do not know what is inside our particular wheel sensors so, to say this:

Originally Posted by FrenchMike

To me , 10 volts mean an open circuit inside the sensor simply ...

is simply conjecture based on the complete lack of technical data available to us. As you do not have the circuit your statement is just what you say it is: a belief. That's not really a good basis for fault finding is it.

Simon, do the test yourself ! IT WORKS .

Are you saying that, with the wheel rotating, your meter reading slowly changes from 0.7v DC to 1.7v DC with respect to earth? What happens when you spin the wheel faster? And what do you think those voltages signify: a working or a faulty sensor, and why?

Also, why choose earth as your reference? Why not measure the output w.r.t. the supply voltage? What will that tell you?

Simon