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[TECHNOPUG]

I've had intermittent TC and ABS warning light issues ever since I've had my Miggy (about 2 years now). They'll randomly come on, usually if I hit a bump in the road but sometimes when nothing untoward has happened. Other times it'll go days without occurring. They clear as soon as the ignition is switched off.

   I don't think that it's an ECU issue as I've never had any problems with the speedo, so presuming that there are loose or dirty connections/sensors which are playing up. Going to be changing the front brakes at the weekend so want to see if I can address this issue whilst I am at it.

  So where exactly are the sensors for TC and ABS? I presume that the TC only works on the rear and therefore that's where the sensors are. Are they the two lead that connect to the back of the diff?

 To clarify; the TC and ABS lights always come on together, never indepedently. If the TC sensors are only at the rear, does that mean that there can't be a fault at the front, which is triggering the ABS lights?

[Andy B]

TC uses the ABS sensors on al four wheels. You're righta bout the rears, the fronts are similar. Just find the castle -ated (sp?) ring on the hub, this is what the ABS sensors 'look at' to determine whether a wheel is stopping faster than the others, or getting faster t han the others in TC mode 

Their plugs clip onto the inner wing next to the low brake pad warning sensors.

[TECHNOPUG]

I assumed the TC only worked on the rears, seeing as they are they only driven wheels.

OK, so in theory it could be any one of the 4 sensors that is returning duff signals and tripping the lights?

I've seen the pad-wear sensors on the front (and I know that they aren't connected - I'm not going to bother getting new ones when I change the breaks either) so hopefully if I chase the wires upto the wing, I can find the offending cause there.

[2woody]

for your '96 car, it's a relatively unsophisticated system.

the ABS and TC are controlled from the same ABS ECU, which is part of the ABS "block" under the bonnet.

there's a speed sensor fitted to each wheel at the front and each diff output at the rear. These sensors are used to :-

calculate the speed that the vehicle is travelling at and to feed this to speedo, stereo, airbags, etc.

calculate if an ABS intervention is required, whereupon the ABS hydraulics intervene

calculate if TC is required, whereby power is reduced

the sensors are a tiny coil of wire, which reacts to the iron in the reluctor ring going past them, kind of like how an alternator works.

usual failure modes are damage to the ABS sensor, a lump of rust stuck to the end of the magnet in the sensor (right adjacent to the reluctor ring) and rust on the reluctor rings themselves.

DO NOT try to remove a front ABS sensor, you will break it.

the front reluctor rings are a part of the front hubs
the rear reluctor rings are a part of the inner CV joint.

half an hour with a wire brush and a magnetic screwdriver should clean them up enough to be trouble-free. If that doesn't work, then it's change sensor time.

[TECHNOPUG]

That's an excellent repsonse, thanks!

It does pose a couple more question though:

Are the reluctor rings obvious (couldn't find any pics in the maintenance guides but will look again)?

And is there easy access to clean them or do they require dismantling of parts (or just jack the car up and remove the wheel)?

[Andy B]

That's an excellent repsonse, thanks!

It does pose a couple more question though:

Are the reluctor rings obvious (couldn't find any pics in the maintenance guides but will look again)?

And is there easy access to clean them or do they require dismantling of parts (or just jack the car up and remove the wheel)?

If you take your disc off you'll see it on the back of the hub. Not sure if you can see it from behind with the disc still in place.  :-/

[2woody]

reluctor ring is just a ring of metal, machined with what look like gear teeth on the outside.

rears are easy to spot because they're on the outside of the inner CV joints

front really require disc removal to see.

[TECHNOPUG]

Found a picture on the front disc maintenance guide. Will I need to remove the backing plate to get to the front of the teeth? It looks like I'll only be able to clean the top of the teeth otherwise. Will that be sufficient? Should I use any kind of cleaner (carb cleaner?) on them to help remove all the crud?

[Andy B]

Found a picture on the front disc maintenance guide. Will I need to remove the backing plate to get to the front of the teeth? It looks like I'll only be able to clean the top of the teeth otherwise. Will that be sufficient? Should I use any kind of cleaner (carb cleaner?) on them to help remove all the crud?

I think the back plate only comes off when the hub is removed, and you don't really want to do that. Remove the caliper (cable tie it out of the way - don't let it hang on the brake flexi) to get to the ring & just use a wire brush. 

[TECHNOPUG]

Excellent, I'll do that as a matter of course when changing the discs and pads. Rears will be easy to access (found a pic of those also). Beginning to look forward to getting my hands dirty at the weekend!

Seems a shame that I'll probably have to move the car on in a couple of months but I'm finding it hard to justify anymore expense on it. Fortunately I got hold of some genuine GM discs and pads a while ago for a good price, so that expense has already been met.

[jonny2112]

The rear sensors are in the diff but the reluctors are elsewhere. The sensors are basically plastic, with nothing really to clean. Is it worth trying to clean the reluctor rings as well?

[Andy B]

The rear sensors are in the diff but the reluctors are elsewhere. ...

 :-? They're exactly where 2woody said they are, quite easily seen if you stick your head under the back of the car

[TECHNOPUG]

Got the brakes done at the weekend. Drivers side was pretty straight forward. Had to move the wheel arch trim to get enough leverage on the carrier bolts. The Pagid pads had a lot of life (at least 50%) in them but the discs were shot. Decided to replace the pads anyway but have kept them for future use.

   The passenger side took a lot longer though as the disc retaining bolt had been over-tightened and it rounded. So I had to spend some time drilling it out and then using a cold chisel and hammer to turn it.

   Cleaned up the reluctor rings and removed all the crud around the sensors. Put the brakes through several heat cycles and impressions were good. Certainly the squealing had gone. Not as much bite as the Pagid pads but they probably need some more abuse to bed them in. Best of all, the ABS/TC lights stayed off for the 90 odd mile journey home.

  Started the car first thing on Sunday and the ABS/TC lights came back on almost straight away Didn't get round to checking the rears so that'll be the next point of call. I guess if after I clean them and I'm still having issues then it's time for new sensors. Any idea how much they cost?

  Oh and my suspected blown exhaust manifold gasket would appear to be more likely a blown down-pipe, as I now have an almost V8 soundtrack....my neighbours are loving me!

[TECHNOPUG]

Actually, thinking about it, I had the CATS replaced last year and they include the downpipe I believe? So it's either the gasket or I've got a cracked manifold. This is starting to sound expensive.....