ABS problem - any pointers really appreciated

[itgoodson]

I'm trying to get to the bottom of a problem with the ABS on my Megane estate 1.6 petrol 53 plate. Here's where I'm up to

The problem started in August. The speedometer would start to wobble after a few minutes driving and then the ABS and Service lights would come on. Then speedometer would return to working normally and the lights would stay on.

After a few weeks of this the lights started to stay on from the moment I started the car, and no speedo wobble at all. That's what it still does now.

I took all four wheels off at this point and cleaned all the sensors and the rings the best I could. Made no difference.

When I took the car in for it's annual service (independent garage) in October I asked them to have a look at the ABS. They said they couldn't locate the problem (he's a great mechanic and I've used him for several years).

I took it today to an independent Renault specialist. He plugged his scanner in but it recorded no fault codes. (have I made a mistake in just using a scanner rather than paying more for a diagnostic test? - I only paid him £10 - I don't know much about diagnostic tests)

Now what should I do next without just handing it over to Renault along with signing over my soul?

All the sensors have been cleaned, no fault codes are recorded, and when it started there was a wobble with the speedometer. My hunch is that there is a dodgy sensor/wire, and I'm tempted to buy a new sensor from Renault for about £25 and and fitting it myself as the next cheapest course of action.

Three questions:

1. Renault told me that there are different part numbers for the offside and nearside ABS sensors. But I might want to try the cable on both sides. Does it really matter? Surely they will be interchangeable? Or is it because the loom on one side is longer than on the other? If so - which side is longest, because I will obviously want to buy the one which is longest so that it will fit both sides when I'm doing my trial-and-error repair!

2. Does the speedometer take it's reading from just one of the wheels, or a combination of two or all four? If it was just one then that would pinpoint which wheel presumably? (though, then again, my speedometer works fine and the ABS light is on, so I'm guessing it takes an average if it is a dodgy sensor?)

3. I'm sure I've read somewhere before that the nearside sensors are prone to go. Is that right?

Cheers for any pointers in advance

Ian

[AlexB]

There are about 50 pages in the manual about ABS. Have you seen them? The factory manual is in the sticky thread above the other threads.

[itgoodson]

Cheers. I'll have to make some time to look through it all... unless anyone knows instinctivly knows the answers?!

[itgoodson]

Hi - I've looked at the Manuals and Technical notes sticky, but from what I can see there is only a pdf relating to ABS fault codes on 4 wheel drives? Should I be looking somewhere else? (Sorry for being slow!)

Could anyone else help me?

- are the front ABS sensors interchangeable? Does one have a longer cable than another (if so, which side?)
- I had a scan done for £10 by a Renault independant. It showed no codes logged. Is this pointing towards a faulty sensor? Should I pay for a more expensive scan, or should I gamble on switching over the sensors as they are prone to go?
- Is the passenger side sensor more prone to failure than the driver side?

Cheers!

Ian

[tomalamix]

it "smells" like ABS wires broken. The speedo uses the ABS sensors for the speed, if i remember right its both sensors on the front. if one is out the other one still gives you the speed but the ABS fault will lit. if both fail you wont have speedo.

a faulty wire can produce continuity when you move the wheel because the wire twists a bit, enough to make the contact on the broken wires.

Remember that outside the wire may look good but inside is what it matters.

good luck

[itgoodson]

Thanks very much. I think I'll go with my hunch on the broken sensor wire. I'll order one from Renault.

Unless someone thinks otherwise?!

[tomalamix]

You possibily dont have one but at least two broken wires, is not common but as you described the things started sometime ago with the ABS light first and after that the speedo went to 0, thats when the 2nd wire caput

good luck

[AlexB]

In your place I would be tempted to measure the resistance of all sensors from the ABS ECU connector.

Thanks very much. I think I'll go with my hunch on the broken sensor wire. I'll order one from Renault.

Unless someone thinks otherwise?!

[tomalamix]

In your place I would be tempted to measure the resistance of all sensors from the ABS ECU connector.

Thanks very much. I think I'll go with my hunch on the broken sensor wire. I'll order one from Renault.

Unless someone thinks otherwise?!

This is a good advise, and not hard to follow. You should do it.

[itgoodson]

Thanks for all the advice. Just to square this one off it turned out to be the cable of the offside ABS sensor. The wheel had been rubbing against it and worn right through the centre of the wire. New sensor plugged in - all working again.


The sensor cost £25 from Renault (cheaper than the scrap yards I tried - some yards said they didn't take the sensors off as they are too hard to get off the hub. I dont know what's hard about it - they just pull off).

[tomalamix]

Only one is broken? Its strange. The speedo shouldn't go to 0 with only one loom broken. You should check the condition of the cable of the other side also.

good luck

[itgoodson]

Just to clear up a bit of confusion, the speedo hadn't dropped to 0, it was working fine. A few months back it wobbled after five mins of driving, then the ABS light came on, and then the speedo returned to working normally. Since August though teh ABS light has been on permanently and the speedo working fine. Did check the other cable though, but that is one is fine.


CHeers

[tomalamix]

oh, my bad then. i thought that the speedo wnet to 0 and stayed there.

cheers