Slightly baffling ABS fault

[r.welfare]

A couple of months ago I posted about the intermittent ABS light on my Accord. A diagnostic identified the NSR wheel sensor was at fault, so I changed it, and the problem went away. Or so I thought.

 

Soooo...here's the weird part. On starting the car the ABS light comes on and goes off, as per normal. BUT - if I then reverse the car straight after startup, it comes on as soon as the car starts to move, and stays on for the duration of the journey, with a consequent loss of ABS (but no other issues with the brakes).

 

If I start off forwards, no problems - and the light doesn't come on if the car is reversed at any subsequent point during the journey. But that's a bit of a faff really - and as the MOT man is likely to reverse it off his ramp to get to the brake tester, far from ideal...

 

So what I do currently is make sure I back onto my drive at the end of the day...no ABS light issues for the last 2 weeks.

 

Multimeter has been out again, there's the right level of resistance at the NSR sensor but, when the ABS light is on, there's no resistance at the corresponding pins on the ABS ECU. Brake fluid level is also OK.

 

My money is on a failing ECU which acts up, at the moment, in the certain circumstances noted above. I've got a secondhand unit to go in (the second time I will have done this job this year, as I had a modulator failure in the 405 in March), but wondered if anyone else had any thoughts before I plow in with the brake pipe spanners...

[eddyramrod]

So what I do currently is make sure I back onto my drive at the end of the day

You surely wouldn't have considered doing anything else? After your driving instructor taught you to "reverse into a limited opening either to the right or the left." Show me the instructor who would teach you otherwise and I'll show you someone who should be stripped of his qualification.

 

And sorry, I have no experience of ABS to assist you; it's much too modern for me.

[r.welfare]

 

Of course, Eddy. But I still can't quite fathom why my ABS unit only functions as intended if the car is driven forwards from "cold", not backwards.

 

Ruddy electronics...

[fiatdaft]

split ring?

 

 

now now.

[r.welfare]

Good point. I fingered it (steady!) to try and discern whether the teeth were all present and correct when I changed the sensor, as it can't be seen without removing the disc from the hub. Will try that first, I think, before committing to changing the ABS unit.

[dieselnutjob]

disconnect the reversing light wiring from the switch in the gearbox and see if it still does it

i have no idea if it's useful in any way but i'm curious.....

maybe the reversing light signal also goes to the ABS controller

[CIH]

check the ring and sensor for any dirt, grease etc

[Split_Pin]

My Vectra's abs rings are old and probably corroded. The traction control light comes on and stays on sometimes, which shares the same rings.

 

About 6 months ago, I hardly used it, and when backing off my drive, the engine management light came on (not ABS right enough though). I assumed that something down in that direction was slightly corroded or damp.

 

Can you get a wire brush to the rings? It might work perhaps?