abs light

It's a fairly safe bet that the hand brake hasn't broken anything, but if you drove down the road with the front wheels turning & the back wheels locked then the ABS will assume the rear wheel sensors had given up.

sherl expressed precisely :

I can't think of anything where leaving the handbrake on, would affect the ABS.

Well it is OK to drive, but there will be no ABS. The ABS carries out two tests...

A static one as you first turn the ignition on, which checks the ABS controller, the wiring and the sensors are within its limits. If they are, the ABS light will go out.

As you exceed around 15mph, it runs a dynamic second test to confirm the signals are coming back correctly from each wheel. If it fails this test, it puts the light back on and it stays on until you turn the ignition off and back on. The second test is carried out frequently as you drive.

Failing the first test could mean a faulty sensor, faulty wiring or faulty ABS unit. Failing the second test could mean faulty wiring or a faulty sensor.

The usual cause of the second problem is damp getting into the waterproof connectors under the wheel arches, causing intermit ant connections. Unplug, squirt of WD40, reconnect and it should be OK. Sometimes if can be a flake of rust on the ABS wheel cog or sensor, upsetting the sensor.

Ok thanks for both replies Actually when this happened I was just round the corner from home (literally) and due to the snow on the road I dont think I got above 10 mph so perhaps it may clear as I go faster the next time?

certainly having some of the wheels stationary and others moving will confuse the abs. I came across this on a VW which had been towed with the front wheels in the air and the ignition switched on. The abs light stayed on, a diagnostic showed that the rear sensors were the problem, clearing the stored codes restored the system to working. I would actually expect that your system should reset itself after a few normal uses, but if not then a trip to a dealer to get the codes read and cleared will do it. The car is safe to use with the abs inoperative for normal driving, but you will not have working abs for emergencies, and of course it will eventually be an MoT fail.

If it doesn't clear after 3 restarts & then disconnecting the battery for a minute (but only if you know the radio code) then you or any garage will need to clear the fault code.

It happens that sherl formulated :

No. It comes on with the ignition then should go off. It comes back on at 15mph if there is a fault.

I've just had another thought on this, now you have mentioned snow...

If it is a front wheel drive, rear handbrake, then it could drag the rear wheels on snow which would throw up an ABS fault.

A few restarts and/or driving with no wheels slipping should probably clear it.

In message , sherl writes

Don't know for sure but you'll probably find it will go off on it's own. The ABS light will illuminate if the module detects no pulses from a sensor and if you had a wheel sliding as you set off, because the hand brake was partially on, that will cause no pulses.

Harry Bloomfield gurgled happily, sounding much like they were saying:

On packed snow or ice, it's entirely possible that the rear wheels were locked and dragging - the ABS will see a difference in speed from front to rear wheels, and will decide there's a sensor problem.

Hopefully it will clear itself eventually but if your lucky it'll stay with no abs until after this spell of snowy weather has gone. For stopping in snow I find abs crap and have more control with cadence braking.

That doesn't help much when only one wheels on ice.

Thanks for all your replies .. I was in luck actually.. it was still on this morning but after driving for a few mins it cleared itself and stayed off

I had this on and off for a while, but eventually the light stayed on. Problem is the wire from wheel hub sensor to the ABS unit. The wire eventually breaks internally due to suspension movements.

Although in Sherls case the wheels not turning would seem a more likely explanation.

I had the ABS light off OK when starting, but always came on when passing a bridge bump on the motorway where M25 crosses over M4. However, the ABS worked fine for 16 years.

It happens all the time during an MOT brake test, it will go out after a short drive.