boxsey911

Second update:

Bit the bullet and bought two rear ABS sensors. Fitted the right rear first and no effect - warning light and buzzer came on just after driving off. Then fitted the left rear and got no warnings on a very short drive. Then proceeded to fit my new front rotors and pads and cleaned the front sensors while I was in there (they were pretty clean). Then cleaned up the plug to the ABS controller, shined up the tail lead to the battery and re-seated the two relays on the ABS pump. Did a 30 mile drive with no warnings.

Not counting my chickens yet though because the problem seems to occur when I drive the car from cold.

p.s. The two new Bosch rear sensors had readings of 1600 ohms!

g60pops

Good result at least.
On a side note, when you redid your interior carpet do you remember if the driver's side seat belt receiver that has an electrical connector on it is connected to the wiring loom?

boxsey911

Mine's not plugged in because it's not long enough to reach now that it's bolted to my Recaro PPs.

g60pops

But originally it is plugged in?
And if yes do you know the purpose?

sundog

Well, they also don't work if this happens to them.

boxsey911

Ah got you know! Yes there is a plug for it. It's the seat belt warning light.

alexjc4

Great stuff! Was that broken sensor the issue then. Wonder how that happened?

Btw these are inductive so it would be the small voltage pulses they generate as the wheel turns that you would measure to diagnose this sort of issue (magnetic tip bust so little or no inductance as the teeth on the hub pass through the field) The resistance tells you if there's a short or open circuit which is a start.

boxsey911

Thanks Alex, as mentioned above I'm not 100% convinced it's fixed yet. I'll be holding my breath over the next few drives. The resistance measurements were all in the expected range (600 to 1600 Ohms) so there was nothing to indicate if one was bad. All looked intact and clean. The only thing I had to go on was that the warning did not come on until I drove off. It would happen within a few yards. So I decided that the only option was replacement one by one. The rears are the cheapest so I started there. At the moment it looks like the second one I changed (left rear) was at fault.

BTW the replacement Bosch sensors have a plastic body and the magnetic tip is flush rather than protruding. They are also a much snugger fit and took some 'persuading' to get them in.

ras62

Sounds like a result Steve! Did you check the ABS is operating?

boxsey911

As said above only a cautionary result until I try it out more.

Yes the ABS works....I have a nice bumpy piece of test road that will fire the ABS if I stand on the brakes. This is the same test road that let me know that my ABS pump unit had packed in a year or two ago! That was a different scenario because there were warning lights/buzzers to tell me there was a fault. TBH I'd be quite happy if 964s didn't have ABS because it's always a PIA to diagnose problems with it.

robt964

>BTW the replacement Bosch sensors have a plastic body and the magnetic tip is flush rather than protruding. They are also a much snugger fit and took some 'persuading' to get them in.

Hi Steve, do you have a part number for these? Having a plastic body makes a lot more sense than the stainless steel of the regular ones. My rear ones had completely welded themselves in place and I'm fairly certain I've rogered them getting them out! (alloy castings and stainless steel don't go together too well)

boxsey911

Rob, the Bosch ones are listed with the original Porsche part numbers. Here's a link to where I got them from:

http://www.design911.co.uk/fu/prod91...or-Porshe-964/

p.s. ignore the photo in the link because that's a picture of the original. The Bosch ones look like this:

robt964

Brilliant, thanks Steve. Ordered them with a bunch of other stuff.

boxsey911

Third update

My optimism is unfounded because the ABS warning is back after the first drive out since everything I tried last weekend. Things on my list to try now are:

Clean up grounds associated with the ABS wiring (I've noticed one very corroded one near the trans)
Check the spoiler warning light bulb in the clock because that's still not working.
Tighten up the alternator belt (I have as suspicion that the problem is more electrical supply than with the ABS components themselves)
Change the coils? (problem is most prevalent when car is cold and I do get frequent stalling for the first five minutes of a drive).
Anything else?

Unfortunately the problem is still intermittent which makes it so hard to trace e.g. The warnings come on after a few yards of driving. If I stop and re-start the engine the warnings don't come back but then if I sit in traffic a little later and pull away the warning will come on again.

ras62

These things are sent to test our patience Steve! ABS earth is located on the drivers side (RHD) inner wing. Maybe a recheck/reseat of R51 is not a bad idea also, along with checking the ABS power supply connection at the battery.