Braking problems

[wazza]

I turned the ignition in my car yesterday and the Brake Warning light in the DIS showed up (the big red warning sign). The ABS light is lit too.
I've only had the discs/pads/fluid changed in July and the pads have plenty of thickness on them, fluid is fine.
I took the car down the road and it seems that mechanically they are OK.

It has been suggested to me that a common fault is that the ABS sensors can get clogged up with dirt/brake dust etc.

1) Has anyone come across this before? [img]images/graemlins/confused.gif[/img]
2) Where are the sensors exactly/can they be cleaned easily? [img]images/graemlins/laugh.gif[/img]
3) It's bad for my liver when the car is out of action [img]images/graemlins/062802drink_prv.gif[/img]

[Carps]

(Assuming you have checked fluid levels)

The ABS sensor disk lives 'in' the back of the disk, so you'd probably have to remove the disk to check/clean it. It is possible that it has got so filthy that the little holes are clogged, but hopefully if you just had new disks and pads whoever did the job would have cleaned the sensor disk before refitting it. It is also possible that the pick up has been dislodged from it's mount and so isn't pointing in the correct direction anymore. Again, probably a disk off job to check it.

One thing that can happen when replacing the disks/pads is that the fluid from the caliper gets forced back up the lines. If that fluid is contaminated (which is quite possible), and it enters the ABS pump/control system then that could cause a problem too. The proper way to do this is to clamp the lines and release the bleed nipples when compressing the piston, so fluid does not pass back up the lines but escapes into a jar that you rig up to catch it in. Ideally this will be followed by a full system bleed.

VAG-COM may be able to isolate it to a sensor or pump problem, if you have access to it...

[SimonS4MTM]

Hi Biturbo

I had the ABS light on in my car at the start of the year.

It turned out to be the abs ecu, about £1000 (under warranty luckily).

Lets hope its not that, good luck!!! [img]images/graemlins/confused.gif[/img]

[wazza]

Get the dealer this morning and do you think the warning light would show? [img]images/graemlins/rocketwhore.gif[/img]
Don't you just hate it when that happens [img]images/graemlins/mad.gif[/img]

Anyway, the dealer did half an hour diagnostics on it, even took it out on the road and could find no faults. In the end they just gave me the keys back and didn't charge me for the half hour. [img]images/graemlins/clap.gif[/img]Well done Executive Audi [img]images/graemlins/bowdown.gif[/img]

[bazza]

was that executive audi in st albans.

I was there this morning too [img]images/graemlins/1syellow1.gif[/img]

[Carps]

That's brave congratulating them for not finding a fault that your car had reported. Did they offer any explanation as to what might have happened ? Did they hook it up to the diagnostics or just test drive it ?

[wazza]

was that executive audi in st albans.

I was there this morning too [img]images/graemlins/1syellow1.gif[/img]

Yep. Between 11 and 12. Parking was as good as normal [img]images/graemlins/tongue.gif[/img]

That's brave congratulating them for not finding a fault that your car had reported

I was congratulating them on not charging me for the technicians time.

Did they offer any explanation as to what might have happened ?

They do not know what happened, as there was no problem when they saw it, but said it could well be the ABS sensors being dirty.

Did they hook it up to the diagnostics or just test drive it ?

both diagnostics in the workshop and out on the road. [img]images/graemlins/thumbs.gif[/img]
They checked the mechanics of the brakes and nothing was out of order. Should the light reoccur I will take it back to them.

[JohnW]

Paul,
if they had checked the fault log it should have showed an intermittent fault log. Chances are they just cleared the log without checking it.
I'd lay money on it being a wheel sensor.

Next time it happens get someone to plug vag-com in for you and have a look.

Cheers, [img]images/graemlins/beerchug.gif[/img]
John.

[Golich]

You can't tell anything from removing the disk. The sensor is well into the hub and takes its pick up from the castelations (spelling?) on the outer part of the CV joints.

I would be very surprised if dirt in the castelations could fool the sensor as it works on the strength of the pulse from the castelations.

The sensors are all pushed into the hub so the best you could do is to ensure they are fully pressed in and tight. However, these sensors tend to become so damn tight that when I attempted to remove both my front ones while removing the whole hub from the car summer past I just knew I was likely to damage the hard brittle plastic that the sensor body is made from. I don’t know how much they cost but my Mazda ones were £90 each! So I opted to remove the wiring from next available plug in the car wiring loom and left the sensor in place as there was nothing wrong with brakes.

I'd be very surprised if VAGCOM or the Dealer's VAG tool can't diagnose an individual sensor as clearly the car reads each sensor individually!

All you can do is check they are all in tight and keep running the car until it happens again and look for the error code.

If a sensor does go faulty all it means is you'll loose the anti skid function. It will also screw up the traction control and stability function. But you'll get the warning lights that they are not working and can drive accordingly.

Something that jsut occred to me. If your dealer does find a supposed faulty sensor make sure he checks the wires and block connector inside the car for a poor connection or damaged insulation from chaffing.