no abs light

robyoz · Unread post by **robyoz** » 03 Sep 2006, 00:23

I have no abs light coming on at all have checked bulb and fuses they are fine any ideas?

Mandrake · Unread post by **Mandrake** » 03 Sep 2006, 01:24

Although I havn't seen the circuit diagram, the ABS light should have some additional circuitry - probably just a pullup resistor.

This is so the light is "failsafe" - the default action of the light is to be on, and the ABS computer shorts it out to turn it off. (Rather than the reverse - providing power to turn it on)

This is done so that unplugging the ABS computer (or the fuse that powers it) causes the light to stay on, rather than stay off.

If possible trace from the bulb and see if you can find any resistors/diodes/transistors/relays connected to it.

Also try unplugging the plug from the ABS computer and turning on the key - if the light now comes on there could be a fault in the ABS computer, if it stays off, the fault is not in the ABS computer, and is probably somewhere in the instrument panel or wiring.

One more thing - does the ABS actually work ? (Does it prevent the wheels locking on a wet road ?)

Regards,
Simon

Unread post by **CitroJim** » 03 Sep 2006, 08:26

I had this on mine.

There is a wiring connector under ABS block and very hard to get to. It has three wires and if this is pulled apart it puts the light out despite the ABS being non-functional. I guess it's a "trick" to try and fool an MOT tester if the ABS is duff. I found my connector to be just half pulled apart and when I reconnected it the ABS lamp came on full-time. One wheel sensor was later found to be dead. I found out all this after pulling the dash apart to check the bulb.

The light is operated from a relay and IIRC it's the pale green one near the ABS ECU. The ECU operates this relay to put the light off. When the ABS ECU goes through it's self test when you first turn on the ignition you can hear this relay clicking and the lamp should flash on an off a few times.

robyoz · Unread post by **robyoz** » 03 Sep 2006, 11:34

Thanx for replys abs def dont work so sounds like previous owner has done something to get it through mot should of thought of that before taking fiddly dash apart