ABS woe

[hinged_bap]

I've had ( intermittent ) low speed brake pedal crunch for some time now, the rear hubs have been renewed - amongst other things ( and the rusty backplates cleaned up to preclude rust flakes attaching to the reluctor rings ) but still no joy. After an inconclusive ABS pulse test session yesterday afternoon. Last night, the ABS fault light came on and I now have a solid ABS fault at static and out driving. This morning, I disconnected the rear o/s sensor ( at the connector at the rear of the back seat ) and connected a new one ( so obviously the new one isn't in contact with the reluctor ring ). My question is, if the rear o/s sensor was faulty, should the ABS pass static test with my fitting a new sensor in this fashion.
TIA
Bap

[rustymotor]

Hi, I'm not expert far from it, it's not passing the static test. Where did the new sensor come from?

[hinged_bap]

Hi, I'm not expert far from it, it's not passing the static test. Where did the new sensor come from?

I bought it from ebay, in fact, all sensors on the car ( of varying vintage ) came from ebay. Never paid more than £15.

[rustymotor]

Hi, only ask because I had read that the ebay ones give a problem..you can check the voltage at the abs wire plugs blue cable should give 12 v momentarily using a cheap voltmeter, might help eliminate the abs unit.

[chris75]

My question is, if the rear o/s sensor was faulty, should the ABS pass static test with my fitting a new sensor in this fashion.
TIA
Bap

Interesting question ! I would say yes it should as the circuit is present and correct whilst not moving , but I've never actually tried this . If you can get a TOAF or a T4 diagnostic test done , that will pinpoint your problem wheel . I have found TOAF very helpful in this respect:}
I am sure I have seen the particular substitution you have tried referred to on here before , but can't quickly find the thread ; a serious search on here might help :shrug:
One last thought , the wheel may need to be spun or driven briefly to clear/reset the static test warning .

[Roverpip]

I've had ( intermittent ) low speed brake pedal crunch for some time now, the rear hubs have been renewed - amongst other things ( and the rusty backplates cleaned up to preclude rust flakes attaching to the reluctor rings ) but still no joy. After an inconclusive ABS pulse test session yesterday afternoon. Last night, the ABS fault light came on and I now have a solid ABS fault at static and out driving. This morning, I disconnected the rear o/s sensor ( at the connector at the rear of the back seat ) and connected a new one ( so obviously the new one isn't in contact with the reluctor ring ). My question is, if the rear o/s sensor was faulty, should the ABS pass static test with my fitting a new sensor in this fashion.
TIA
Bap

Hi Bap, some interesting info here:
http://http://www.macfadyen998.plus.com/

I had problems with my ABS not so long back. In answer to your question; ABS does a 4 sec test - ECU sends signal to each ABS sensor. If all ok, ABS light goes out, however if after driving a short distance, a fault occurs then ECU registers fault & illuminates ABS light.
If an ABS sensor goes faulty, then the ECU cuts power to the affected unit.

The test is in 3 parts.
1) strip back part of the cables into the ABS plug (see website link for colours)
solid colour is 12v constant, striped is pulse (could be other way round lol)
Using a volt meter, connect + to 12v constant - to good earth, this should give you a 12v reading.

2) raise relevant wheel off the ground. Connect voltmeter + to pulse cable - to ground. Spin the wheel and check readings - 0.67 rested & I think 1.74 with wheel turning. This determines sensor is reading the ring.

3) You'll need a donor set of ABS plug/socket. The idea is to 'bridge' the affected ABS to a known good cable i.e NSF ABS plugged into OSF socket. Its a way of kidding the ECU & usually works & can be good at determining faulty cabling.

My problem was a break somewhere in the loom. In the end I took new cable from the ECU to the affected ABS - hey presto, working ABS again.

Check under the battery compartment tray as this is where the ABS ECU lives & can get water damaged from plenum drain issues.

Another idea would be to disconnect the battery for 30 mins - as this can sometimes reset the ECU.

Hope this helps,
Phil.

[cb750chris]

Hi David,
If you need any further hep with this, give me a shout and I will try and give you a hand - I can plug your car in on the T4 and we can home in on this fairly quickly (hopefully).
We can certainly sort this out, just a matter of time :)

Regards
Chris

[kaiser]

I have had my ABS light on and no speedo for quite a while.
Yet the cruise function worked.
Yesterday I decided to give it some serious attention.

I took ear buds soaked in acetone, and cleaned the ring in the sensor hole. I know the front right wheel is responsible for the speedo.
The sensor senses from the side, so you try and clean the side of the bearing with the cotton bud while turning the wheel hub.

I must have used 6 buds both ends, and a lot of black greasy stuff cam off.
I tried a couple of times putting the wheel back, but no joy.
Then I dismantled the blue connector inside of the plastic wheel protector and sprayed some WD40 into the plug, and assembled it with a firm pressure.

Wupti, speedo works, ABS light gone.:D

So pay attention to the connector as well as the sensor. There is further a connector under the front seat that can give problems, but I didn't have to attend to that.

[rustymotor]

I had the same problem with a Vauxhall 2 days before the MOT, cleaned the plugs with wd40 and bingo abs light gone..

[lesternester]

I had also been having intermittent low speed brake pedal crunch and sometimes the abs light came on but last week my battery light came on and the alternator wasn't charging at all,i ran the car all week by charging the battery up every night,the thing is all week i've had no brake pedal crunch or abs light,yesterday i repaired the alternator with new regulator and brushes and the abs problems haven't reappeared.Maybe irregular power output from the failing alternator could be the cause of the abs problems.Just another thing that you could check,i had the same abs poblems on a previous 75 and never did cure the problem.Good luck.