Any autoelectricians? ABS/earth issue Q SOLVED

[r.welfare]

I've had intermittent ABS issues with my Accord for 5 years or so (year 2000, 1.8 hatchback auto).

 

When the ABS light first started coming on, I read the fault code and it indicated an open circuit on the nearside rear sensor. So I ponied up £200 to the local dealer for a new one, fitted it, fixed the fault for a couple of months. Then the light came on again.

 

It didn't stay on all the time; sometimes it wouldn't go out when the ignition came on after getting into the car after leaving it a few hours, other times it would come on while driving. It seemed to be more of an issue in the winter months, which was good because by the time spring (and MOT time) came round it would be well-behaved.

 

I read somewhere that the (Bosch) ABS pump/modulator (it's an all-in-one affair) can get a bit cranky over time, so I replaced that with a secondhand one a couple of years ago (that was a fun job). This put the light out for months at a time, in fact bizarrely the car went through this winter with no light coming on (other than on startup, then going out properly after 2 seconds) at all. But every so often the problem would return, intermittently.

 

For the last two or three weeks it's been on pretty much constantly. Again, the paperclip diagnostic test indicates the same nearside rear sensor open circuit fault. Sometimes, if you shut down and restart the engine after a few minutes, it will go off and stay off - but only for a few miles. And you can hear a chattering from the pump when braking at low speed.

 

Here's the weird thing, which makes me think it's an earth fault - if it goes off on startup, 90% of the time it will come on again once you've used the windscreen washers. Seriously, it's barking.

 

So, what I've done:

• Undone, cleaned and tightened up the two obvious earths (one underneath the power steering fluid reservoir, one on the nearside front strut top);
• Checked the multiplug on the modulator for corrosion, sprayed in some contact cleaner, and added some dielectric grease;
• Disconnected the plug for the nearside rear speed sensor and checked the resistance - comes up with 1600ohms which is within an acceptable range according to my Honda workshop manual CD;
• Checked also the resistance of the offside rear, which shows no fault - that's near-as-dammit the same value of 1600ohms;
• Removed the nearside rear ABS sensor from the rear hub, wiped off any dirt and iron filings from the magnet, cleaned up the mounting hole and backing plate with a Dremel to remove rust so it fits nice and snug;
• Had a look at the toothed wheel on the hub for any damage to the teeth, cracks or dirt/grease - all looks OK to me;
• Checked that the magnet in the sensor is picking up the wheel by spinning the hub and seeing if I get any voltage through;
• Had a look at the wiring from the connector back into the inside of the car - it passes into the body under the rear seat then joins more wiring under the sill trim, can't see any obvious breakages.

What I haven't done:

• Checked for continuity or shorts to power/ground between the connector in the nearside rear wheelarch and the ABS pump/modulator. I've got instructions in the workshop manual on how to do this, so if I get a chance I'll have go;
• Checked the battery voltage. The battery was new about six years ago. Never fails to start the car, but I did have a slipping alternator belt recently;
• Torched the bloody car.

To be honest I can live with it until next March's MOT, but having had a near miss the other morning due to a combination of my own stupidity and that of other drivers (the impressive skidmark on the road was matched by that in my underwear), it would be nice to fix it if poss; I'm fond of the car, it's been a faithful servant these last six years in my hands and for the five years my dad owned it before that, everything else works (a/c blows cold etc), mechanically it's spot-on and it should hit 200k fairly soon which would be a nice milestone to reach.

 

I am contemplating taking it to an auto electrician if it's likely to be an earth fault but wonder if there is anything obvious I am missing...(other than a need to be a more cautious driver). However, if anyone is knowledgeable and thinks it's likely the "new" ABS pump/modulator is suffering from electronic Alzheimer's then I may as well not bother and run it until the ticket runs out.

[Albert Ross]

Check the wiring to the sensor... it may have a slightly weak/bent connector in one of the plugs. Simple but often missed.

[r.welfare]

Couldn't see anything obvious but I'll give it a tweak if I get time over the weekend.

[rml2345]

If it's the same system Volvo used they can be very sensitive to battery connections. Either that or moisture is getting into it somehow and making it go potty?

[r.welfare]

Hmm. Connections all seem OK and I've traced the wire into the car from the rear wheel arch to where it joins other wires under the near side rear door kick plate. No obvious breaks or corrosion.

 

I swapped the modulator electronics over with another secondhand part (fun job, that), still the same issue, although the light stays out longer upon restarting the car and driving off before it comes on again, if you see what I mean.

 

The fact that I can communicate with the modulator with the paperclip diagnostic trick leads me to believe the modulator itself is OK.

 

Booked in with an auto electrician (an old school one, rather than an ICE specialist) for next Thursday, so let's see what he finds.

[r.welfare]

Now solved. Auto sparky diagnosed a broken wire up near the fusebox so has sorted it all out. Nice to have an ABS light that behaves itself, and a firmer brake pedal to boot.

[Mr_Bo11ox]

How do these boys find this stuff. Great work man.

[r.welfare]

I know, I think the lad worked from the ABS ECU back whereas I was going the other way from the sensor towards the front! He charged me 2hrs of labour so not too bad, particularly if it puts to bed an issue which has been happening off and on for about 5 years.