ABS warning light

[dvisor]

Hi - My ABS warning light has started to stay on after starting the engine. The problems started a week or two ago. I did a 100 mile trip, and it was fine. Before returning home, I noticed that the drivers side headlight was blown, so I replaced the bulb and drove home. It was during this return trip that the ABS began to play up. I'm wondering if I disturbed anything while changing the bulb, but as far as I know, there is nothing around that area that relates to the ABS. I'm not really sure how to go about testing the ABS sensors (or how to get to them), but reading another thread I understand there's a connector block near the coolant reservoir which is worthy of checking. Unfortunately, the photo links are broken. If anyone has a real idiots guide for troubleshooting the ABS I'd appreciate it. MOT is looming (always the way when you get a problem, isn't it), so maybe its best to leave it in the hands of a pro anyway.

[g8dhe]

If the light is flashing then start with the diagnostic connector and use the flash codes from there to start with at least that should indicate which sensor it thinks is faulty (assuming faulty sensor of course!) http://www.philmcfadden.co.uk/MazdaDiagnosticBox.htm

Once you know which one is perhaps faulty then check the resistance of the sensor with a multi-meter, however its not always a totally broken sensor, so it doesn't always test faulty in which case it might be replace and hope!

[dvisor]

Thanks for that, Geoff - really useful, and I'll give it a go. The ABS warning light isn't actually flashing, but staying on (on a couple of trips it did go out for a while, but came back on again a little later). Presumably the LED the page refers to is a simple 12v LED with trailing leads and no resistors.

[g8dhe]

If the LED is rated for 12v yes (it contains the resistor inside).

[dvisor]

I finally got around to checking with an LED via the diagnostic connector (thanks Geoff), and it looks like it's the right front wheel speed sensor. I can't help thinking its a coincidence that it happened at the same time that I replaced the right side headlamp. Is there any wiring around the headlamp related to the ABS? Other than that I'll get the garage to take a look at the sensor at the same time I get the MOT done. Thanks.

[Bongolia]

I finally got around to checking with an LED via the diagnostic connector (thanks Geoff), and it looks like it's the right front wheel speed sensor. I can't help thinking its a coincidence that it happened at the same time that I replaced the right side headlamp. Is there any wiring around the headlamp related to the ABS? Other than that I'll get the garage to take a look at the sensor at the same time I get the MOT done. Thanks.

You will have to in order to get the MOT.

A quick initial check routine I use is as follows;
Scan to indicate what/where the fault is.
Engine off.
Check all tyres are the same rolling radius and inflated correctly (they would have to be almost flat in reality)
Remove the road wheel from the side displaying the fault
Check the reluctor ring (the toothed ring) carefully for cleanliness,freedom from cracks or missing/blocked teeth and that the ring is secure.
Clean the face of the sensor with a carb cleaner type spray
Check the wiring by following it back from the sensor to the first connector for any breaks (unlikely)
Disconnect the sensor at the plug and connect the sensor side to a multimeter set for AC
Replace the wheel and rotate it as fast as you can you should see a voltage here of between .50-1 V or better it will be higher the faster you can spin the wheel.
If any of the above are not correct replace/fix them.

Clear out the codes from the ECU ( dont know how you do this on the Bongo but disconnecting the battery and putting the ignition to cranking and depressing the brake pedal works on some vehicles,reconnect the battery after a few minutes) switch ignition to run position but not cranking, look for the light.
If its still on then let the garage have a look.

As your light illuminates when the engine is started and not after/during a run it is likely its failing its preliminary checks. As your fault first showed itself when driving it is likely to be that the signal was failing and that you have indeed got a duff sensor or a break in the wiring to the ABS block likely the former.

P.S.
In practice when trying to remove an old sensor from the hub it will become damaged so its not normally possible to check the sensor off the vehicle so dont be tempted to take it out to clean it.
Good luck and let us know the outcome.

[Northern Bongolow]

when you say right side headlamp, which do you mean. the abs unit is a way back behind the passy side headlight so you may have moved the plug to it.

someone else on here had a fault on the abs and just removed and cleaned and refit the plug that sorted theirs.

[mikeWalsall]

That was me .. The dealer had removed the bulb to mask the problem but as none functioning warning lights are an MOT failure .. me and my son had to sort it out ..

Mostly by luck (and a multi meter) we found it was a bad connection in the multi pin connection from the ABS valve block behind the leisure battery..

[Northern Bongolow]

thats the fella , you had some pics too if i remember right.