ABS wiring

Philip Chidlow · Post by **Philip Chidlow** » Tue Apr 18, 2006 5:12 pm

I have an intermittant fault on the ABS - the light stays on more often than not. However, the last time this happened, a couple of months ago, I checked the (electrical) connections on the ABS block next to the n/s wing - after a bit of wiggling and cleaning the light stayed out and all was well. Until yesterday when the light stayed on. Now, again I did a bit of cleaning and fiddling and it stayed out for half a mile or so, but another pothole jolt caused the ABS light to come back on again.

I am considering removing the air box to get better acces to the wires, but I am having some difficulty in identifying the wires. I have two big connectors with a feed from the battery and another brown connector block burried deeper down. There is also a wire with an inline fuse. Main connection to the ABS block comes from the former, (and getting that connector off the ABS block looks like it could be tricky as I don't want to damage anything). There is another connection to the ABS block next to that at an angle which likewise I don't want to disturb unless I know it's safe to do so. The earth seems fine but I'll clean that up too.

Am I wasting my time and is it just a coincidence and actually the fault lies at the wheel(s) I wonder. At least if I can clean it all up it might work. But again, I want to know what it is I'm taking apart and reconnecting!

As you can tell I know very little about car mechanicals/electricals but I reckong if I make sure everything's connected as it should be, clean with good contacts that's a start!

jeremy · Post by **jeremy** » Tue Apr 18, 2006 5:23 pm

I can't see you will do any harm taking the connectors off the control block, carefully cleaning them and replacing them - after all they are meant to come apart and from what I remember can't be got on in the wrong place as the connectors are different sizes.

Intermittent sensor faults are very difficult to trace - I did mine with an audio amplifier - connected the sensor to a jack plug and drove round listening to the hum, till I heard crackles.

You could do the same with a cassette recorder - just have to remember which sensor you were listening to when you played the tape back.

jeremy

ken newbold · Post by **ken newbold** » Tue Apr 18, 2006 5:35 pm

Chances are it's one of your wheel sensors, uusually a front one, or at least the wire lead.

Try following the wires back from the wheels and you'll find a plug located just within the engine compartment, I 've known these be the source of the problem.
Once unpluged, if you have a multimeter you can test the resistance of the sensor from here. You should get a resistance of between 800 - 1400 ohms.
If either sensors is outside these readings, it's no good. You may be lucky and it's just a dry connection.

Way2go · Post by **Way2go** » Tue Apr 18, 2006 5:45 pm

Ken's answer is good. After all, this light is intended as a diagnostic of the condition of the wheel sensors.

Jaba · Post by **Jaba** » Tue Apr 18, 2006 10:49 pm

It is almost always a wheel sensor fault that causes this. Check the front sensors for security then look for an o/c in any of the four coax leads.

Just connect a meter and look for around 1Kohms and then any resistance changes when you wiggle

the cable and connectors.

If that fails then check out this very thorough diagnostic procedure ...

http://www.woollard.com.btinternet.co.u ... ad.htm#ABS

Good hunting.

Philip Chidlow · Post by **Philip Chidlow** » Tue Apr 18, 2006 10:50 pm

I will have a check - once I get a mo. And it stops raining! Thanks chaps

AlanS · Post by **AlanS** » Wed Apr 19, 2006 1:45 am

Common one I've found is the bracket that holds the sensor lead as well as the brake line and is held onto the strut with 4 cheeseheaded allen screws. It also has a wire loop on it to hold the handbrake cable off the tyre.
It snaps through stress and allows the coax to vibrate merrily until it creates an internal break.
I had one that drove me insane and I had it sorted (I thought) several times after I had been working on wires and plugs under the bonnet. I eventually discovered an internal break that would operate sometimes if the cable was in the right place, but all it took was for me to turn on one lock and on would come the light.
New sensor and new holding bracket solved it.
I've also noticed that for some reason, the front passengers side sensor seems to be the one most likely to fail.
I also keep my serratted wheels clear of rust and grit as these will also make some strange things happen.

Alan S

Philip Chidlow · Post by **Philip Chidlow** » Wed Apr 19, 2006 8:35 am

Thanks Alan. That seems like a fairly quick visual check that will (could) help me get to the root of the problem quicker.

I'd do it now, but the wife's driven off in it! (I trust she'll be back

)