PDA

View Full Version : abs light always on mot failure...


Aaron
19th October 2010, 15:15
as above
failed the mot on it

so i cleaned sensors and its still on.

on ignition its always on also...
any ideas???

Woody91
19th October 2010, 15:36
Tried changing the sensors if its not that then could either be a break in the wiring somewhere or the abs module itself.

burgerfeet
19th October 2010, 15:42
Likely to be a failed wheel sensor. Quick tests you can do....

***FUSE***
1. Check that the fuse hasn't blown for the ABS circuit.

***VOLTAGE***
1. Make sure the battery voltage is good and the car is charging properly. Low voltage will put on the light and keep it on.

***RESISTANCE***
1. Disconnect each wheel sensor and measure with a multimeter on the lowest ohms setting. Any sensor that indicates noting (no reading) or very high compared to the others is faulty.

*** WHEEL SPEED ***
1. Disconnect each wheel sensor and connect a multimeter set to read AC volts.

2. Now spin the wheel pretty quick and you should see a small AC voltage appear on the meter whilst it turns.

3. Repeat the test for each wheel and try to spin each wheel at the same'ish speed to compare voltages.

Any sensor that is not working will produce no or an obviously different voltage to the others.

Hope that helps...

Other than that, diagnostics is the only way.

Ross
19th October 2010, 15:50
take the bulb out/mask the bulb. They don't test the abs function, just the brake force.

Job done.

Aaron
19th October 2010, 17:42
^^
they failed it on the abs light not coming on which was the bulb so i put new one
then its always on...

burgerfeet
19th October 2010, 17:52
take the bulb out/mask the bulb. They don't test the abs function, just the brake force.

Job done.

WRONG!!!!!! If the vehicle is fitted with ABS it should function, as in the light should go out. You are partly correct in that they test the brake efficiency which does not test the ABS. If the MOT tester sees the ABS pump and the light is not operational, it will FAIL!!!

Maybe you will be lucky and get away with it.

Ross
19th October 2010, 18:16
Can you point me to where there's a requirement to open the bonnet for an MOT test as I can't find one.


^^
they failed it on the abs light not coming on which was the bulb so i put new one
then its always on...

Gotcha - that would make sense as that is part of the test (coming on with the ignition) but it's frequently overlooked. Although tbh most of the MOT stations I've ever used aren't... how do you say... quite so thorough ;)

Aaron
19th October 2010, 18:38
how do you remove the rear abs sensors on a vts?

burgerfeet
19th October 2010, 19:49
Can you point me to where there's a requirement to open the bonnet for an MOT test as I can't find one.




Gotcha - that would make sense as that is part of the test (coming on with the ignition) but it's frequently overlooked. Although tbh most of the MOT stations I've ever used aren't... how do you say... quite so thorough ;)

The bonnet will be lifted to check for corrosion around the suspension strut tops, check that the VIN is present etc.