Chasing ABS fault

[Mike Noc]

Originally Posted by sworks

Incidentally my car has just started doing this too but as soon as I drive T4 stops communicating. I don’t really want to fire the parts canon at it so I’ve parked I up for another day and I’m using one of our other cars

I've had that on my car Mark, but if I keep below 15mph the T4 continues to communicate. Strange.

Originally Posted by r44flyer

Not T4 but an Autel 808... smooth graphs for all 4 sensors but the pulsing is not so pronounced at the moment, so it's verging on intermittent.

It's definitely cyclical, not random. So now I'm thinking a bearing is breaking down. Brake discs? Possibly but they're either warped or not and would always be bad and never better at times surely?

Yes if it is cyclical then probably one or two of the magnetic reluctor segments are weak and not always being sensed. A generous air gap between the sensor and reluctor won't help though, so worth checking they are correctly seated.
Can't see it being a brake disc problem - as you say it would neither come and go or only happen at low speeds if it was.

[r44flyer]

Originally Posted by Mike Noc

I've had that on my car Mark, but if I keep below 15mph the T4 continues to communicate. Strange.

Same story with the Autel, so I presume the car locks it out.

[sworks]

Originally Posted by Mike Noc

I've had that on my car Mark, but if I keep below 15mph the T4 continues to communicate. Strange.

Originally Posted by r44flyer

Same story with the Autel, so I presume the car locks it out.

I didn’t know that? I must of stayed below 15mph whenever I’ve done it in the past

[Terry00H]

I had what I could only describe as break crunching . This would happen randomly at slow speed .I bought :
75 / ZT Rear Brake Disc Backplates, Shoes & Adjuster Kit - SMF100201 / SMF100211 / SFS100190 / SXS100000 / SMN100290 / SMN000140 MG Rover

From
Discount MG Rover Spares for £130 .Since fitted over two years ago I have not had any break crunching . These corrode and moisture gets in causing this fault .The T4 showed no fault codes .

I hope this helps.

[BigRuss]

Originally Posted by Mike Noc

I've had that on my car Mark, but if I keep below 15mph the T4 continues to communicate. Strange.

That's the way it's supposed to work Mike, as soon as you go over 15mph T4 loses comms

Usually you're looking for a difference in the rotation speed on one of the wheels but it can be very subtle. Really it needs to be done on a flat straight bit of road.

If it's only happening above those speeds it's a lot more difficult to pinpoint unfortunately. As you say the only thing you can do then is to inspect everything visually or get a meter on each sensor rotate the wheel and check it that way.

From experience if the car has been stood for any length of time it's usually one of the back ones that's playing up, and the usual cause has been corrosion build up on the face of the bearing or the backplate. It's hardly ever the rear sensors themselves unless they've become damaged.

Russ

[JosephJ]

I had a very similar issue too. It turned out to be the rear offside hub that had become a little crusty. The sensor was fine which I only found out after replacing it 🤦. Symptoms mainly included a grumbling when coming to a stop but not so much in reverse for some reason...

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