ABS problem

[DanFlo]

I have a Y reg VW Polo and the ABS warning light has been coming off and on since it was purchased over 6 years ago. Over the weekend I had an MOT done and the ABS warning light came on during the test (normally off most of the time) so it failed the test. They fitted a new sensor having run diagnostics, and passed the car. The warning light came back on tonight.
1. Can a car fail with this fault? I know the brakes are fine with the warning light on.
2. How many sensors are there on a car, 1 or 4?
3. Did they do the work? I know the warning light can be cleared using a diagnostics system.
Thanks for any advice.

[Hymie]

Yes, a car will fail the MOT if the ABS warning light is lit.

I know of someone who removed the bulb prior to MOT test - to avoid it failing on this point.
They should check that the ABS light is on during the ignition sequence - but they don't.

[fighter998]

Yes Hymie is correct an illuminated ABS warning light will cause a vehicle to fail the MOT test.
As for sensors, each wheel will have a speed sensor each linked to the ABS ecu, but if you are saying that the light illuminates randomly, i would suggest it is not a sensor. best is take to main dealer and ask for 1 hours worth of diagnostic work to track the problem.
When you have the result from the main dealer, go back to the garage who fitted the replacement sensor and get them to rectify the fault diagnosed by VW dealer FOC.

This is standard industry practice for intermittent fault probs, small independent garages tend not to have the diagnostic experience and always jump straight to replacing sensors which is not always the cause of the fault.

By the way, i can speak with authority as a motor vehicle apprentice trainer for numerous vehicle manufacturers.