robt964

Voltage regulator/ impending alternator problem? Could be over voltage? The additional load of the lights will pull it down. What does the battery voltage read whilst the engine speed is above tickover with everything electrical off?

boxsey911

Rob, I too am coming round to it being a voltage supply issue. The controllers are apparently very sensitive to voltage. The only reading I've done so far is 13.85 volts on idle. I've not been able to measure it above idle yet but will get someone to help me check that out. It's at least 8 years since it's had an alternator change. I presume the voltage regulator comes as part of a reconditioned alternator?

robt964

Yes, it'd be build into the alternator.

robt964

Actually, a few things you could try to indicate/isolate noisy electrical supply caused by engine/alternator.

You've said the light always comes on after the car has moved off?

How about stop on a hill (nose down), in neutral, everything electrical off, ignition on but engine off. Take you foot off the brake and roll away. Does the light come on?

Try again but but this time with the engine running (still in neutral), don't touch the throttle.

Try a third time, engine running, in neutral except this time once the car hits 10mph or more lift the throttle.

Worth a shot.

boxsey911

Some good suggestions there Rob.

I don't think the first test will work because the ABS light won't go out unless the engine is started.

Just need to find a quiet hill to try out the others now.

robt964

>
I don't think the first test will work because the ABS light won't go out unless the engine is started.

Hmmm I wonder how it detects this. It could either be a signal from the Engine ECU or that the supply voltage is less than 13v (guessing the value) as the alternator is not charging. Might be time to look at the wiring diagram as this may be helpful in the diagnostic and possibly simple enough to be 'fudged' to fool the ABS ECU into thinking the engine is running.

Failing all this you may need to find a good auto electrician, somebody with a fluke 120 scope or something similar so the voltage can be sampled and visualised. Regular multimeters will only get you so far. They won't be able to show you a noisy line.

time666

Hi steve,

Right managed to get them out to the PO in time, so 2 abs sensors should arrive with you tomorrow mate, (posted 1st class) so give them a go.

I shall bank 1 pint of the finest guest ale on account for you

boxsey911

A man of good taste.

boxsey911

Update Five:

The ABS has now been working without faults for a week now.

I decided to check the wheel sensors one more time but this time by checking the resistances at the ABS controller plug (thanks ras62). The left rear came up with no reading at all while the other three gave good readings (1,000+ ohms). I then checked resistance at the left rear by unplugging the sensor and putting the meter on it. This came up with a good reading when measured directly (1600 ohms). Plugged it back in and went back to the controller plug. No resistance still. This is a new Bosch sensor that I put in before to try and solve the problem (see page 2). So unplugged it and plugged in a used sensor (the original that I'd removed from the right rear). Now I had resistance at the ABS plug! So I removed the new Bosch sensor from the hub and put in the good used one. No ABS warnings on the first drive or any drives since.

So in summary: I had a bad left rear sensor. I fixed it by fitting a new sensor but that new sensor stopped working within a few miles. Changing it again fixed the problem.

The moral of the story for me is that wheel sensors can indeed stop working but it's best to check them out at the ABS controller plug to find the one causing the problem.

robt964

Hi Steve - glad you've finally got the problem sorted :-)

Couple of questions or have I missunderstood your post?

>
I decided to check the wheel sensors one more time but this time by checking the resistances at the ABS controller plug (thanks ras62). The left rear came up with no reading at all while the other three gave good readings (1,000+ ohms).
>

Ok, so no connectivity at all. This suggests either the sender or the loom between the sensor and the controller.

>
I then checked resistance at the left rear by unplugging the sensor and putting the meter on it. This came up with a good reading when measured directly (1600 ohms).
>

Ok, this suggests that the sensor is not the cause of the break in continuity.

>
Plugged it back in and went back to the controller plug. No resistance still.
>

Ok, as you know that the sensor still has continuity, this points to an issue between the connector on the trailing arm and the controller.

>
This is a new Bosch sensor that I put in before to try and solve the problem (see page 2). So unplugged it and plugged in a used sensor (the original that I'd removed from the right rear). Now I had resistance at the ABS plug!
>

Bingo - You've proved it wasn't the sensor (from a continuity perspective) as when both new and old were tested locally (at their socket) they both had a reading.
I think this still points to an issue between the sensor connector and the controller.
If the poor connection were in this plug on the trailing arm (the most likely suspect), this repeated connection/disconnection from swapping out sensors could have easily resolved the issue?

>
So I removed the new Bosch sensor from the hub and put in the good used one. No ABS warnings on the first drive or any drives since.
>

I bet its the connector :-) If both sensors when tested locally had continuity, but one didn't when tested at the controller, the problem *has* to be with the plug/socket interface on the trailing arm.
I bet if you swapped the sensor back to the new one, and sorted the connectivity issue (should it still exist) (dirty contacts / difference in manufacturing tollerances of the new and old plugs?) it'd work :-)


Of course, you might not care now as its fixed and working. Can I have you're new broken sensor then? :-p

boxsey911

Hi Rob,

When I got no resistance for that sensor at the ABS controller plug I too thought..damn the problem is somewhere in the wiring between the controller and that wheel and was about to set about working my way through it. However, plugging in another sensor at the wheel gave the expected reading which indicated the wiring must be OK.

There's definitely something wrong with that particular sensor because I also plugged it in to the opposite wheel and got no resistance when I measured the appropriate pins for that wheel on the ABS controller plug. My guess is that there is a problem with the white plug on the sensor preventing it from making continuity when it's plugged in. I've sent it back to the supplier and asked for a replacement.

robt964

I have two new Bosch ones on the rear also. I'll be running the same checks as you

HiWind

wow this was an epic sherlock 'olmes thread! A Thrilling DIY read

boxsey911

Yes it was!

I think it told us two things:

1. Something unexpected can lead to you chasing your tail - in this case a new sensor that turned out to be a dud.
2. The value of input and suggestions from others to help you unscramble your own thoughts.