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Old 11th May 2021, 10:23   #11
Mike Noc
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Time to get back to basics Glenn. Courtesy of French Mike you can check all the ABS sensors and magnetic reluctors in the wheel bearings using a voltmeter.
The signal voltage changes from 1.7V to 0.7V as each magnetic segment passes the sensor, so jack each wheel in turn and slowly rotate it marking the switch points on the tyre wall with chalk. You should end up with 48 chalk marks looking something like this:



If any gaps are in the same place each revolution then likely a damaged reluctor, and if in random places suspect the sensor.
Other common failure causes are cable damage to the sensors, flakes of corrosion interfering with the sensing, or corroded plug pins at the ABS modulator. This was the rear wheel, and you can see the sensor was missing more than a few segments:



You connect the positive probe of the multimeter to the signal wire, and the negative to chassis earth:



I made up a cable from some old bell wire and a scrap ABS plug and socket to save pinning through the cable insulation. Here it is testing a hub prior to fitting:

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Old 11th May 2021, 11:53   #12
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Thank you, Mike. Yes, you're right.

I asked my friend to check the plug contacts at the ABS Modulator. Last night - after I asked him to do that - I remembered something. I had a 1992 Infiniti Q45 years ago. It had TCS (Traction Control). The relay for the TCS was mounted under the battery tray. It seems after years of the relay and contacts breathing the battery venting fumes - maybe a tiny amount over a long time - as well as road grime moisture getting through the radiator, it affected the function. It was intermittent like the ABS is this time. I pulled the relay and cleaned the contacts and it was fixed.

Considering our ABS modulators are under the battery tray, I think that's justifies it being the next step. If that doesn't work out then it's on to French Mike's test. Thank you for including that in the post. I knew it existed, but had forgotten the details.

Glenn
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Old 12th May 2021, 19:46   #13
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Hi folks,

We have some progress of sorts. It is consistently leaving the ABS warning light on at the cold start in the morning. Then after a short drive and restart the warning light stays off and all is normal.

Yesterday I asked my friend to start the car this morning and NOT move it. He let it run idle for 10 minutes. The warning light had stayed on as usual.

After 10 minutes he shut off the engine and restarted it. On this restart, the ABS warning light stayed off. Because of this we are 99% certain there is no problem with any wheel hub or sensor. It seems the underhood temperature with a warm engine is the key. So, we'll get it through the MOT and I will give the ABS Modulator plug contacts a good cleaning when I am there the next time.

Cheers,
Glenn
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Old 12th May 2021, 20:13   #14
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My 260, the previous owner had problems with the ABS and Chris @ Retro Sports Cars discovered dry solder joints within the ABS unit. He repaired them but it wasn't a long term fix, ABS light returned during my test drive so the test drive involved a short diversion to see Chris and book the car in! Previous owner ended up replacing ABS unit before I bought the car.
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Old 12th May 2021, 21:10   #15
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Be very careful cleaning the connector pins they bend and break very easily,don’t ask me how I know!
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Old 12th May 2021, 23:09   #16
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Thanks guys. Hopefully it is not cracked solder joints within the Module. As for the contact cleaning, generally I find spraying electrical contact cleaner into the plug, then re-connecting and disconnecting the plug a couple or three times effectively cleans the contacts. Nothing too physical or intrusive.

Cheers,
Glenn
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Old 17th May 2021, 12:24   #17
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Default Passed STK (MOT) but...

Hi folks,

She passed her STK this morning, but with an advisory for the hand brake. I will have to get one of Arctic's modified compensators. It will be at least the end of summer before I get there and God knows when I will have time to address the snags - hand brake, ABS Modulator, right front door actuator and fuel level sender.

About that ABS Modulator - if cleaning the contacts does not fix it, are they reliable enough to trust one from a Breaker? Also, are they the same on the saloon as one the estate?

Thanks,
Glenn
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Old 17th May 2021, 12:37   #18
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As long as it doesn’t have traction control apart from the V8 there appeared to be only two choices from Rimmers luckily mine was without tc so only £105 delivered but then I am a bit more local!
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Old 17th May 2021, 12:49   #19
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Quote:
Originally Posted by 3disco View Post
As long as it doesn’t have traction control apart from the V8 there appeared to be only two choices from Rimmers luckily mine was without tc so only £105 delivered but then I am a bit more local!
Wow, that is way less expensive than I expected. Thank you 3disco!
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Old 17th May 2021, 13:43   #20
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There is a new one on eBay from a garage for £40 +£5 postage or make an offer!
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