BMW 5-Series E34 (1987 - 1996) - 89 3.5 535 Sport ABS Issue

Honest John Back Room » Technical matters
View Threaded
Thu 15 May 2008 20:59
89 3.5 535 Sport ABS Issue - thomp1983
Evening folks,

as above having problems with the abs on my 535, basically the story goes, removed the rear axle to replace some bushes and also run some new brake lines as the old ones had corroded. once reassembled everything was fine but then after a couple of days the abs light came on. i assumed it would be a piece of dirt had come lose of the hub rings and got onto the sensor causing it to flag an error, removed the sensors and sure enough there were a couple of large bits of rust stuck to the sensor. removed them reassembled again and the light was out so thought all was well. a few days later i ran the car up to warm on the drive the other day whilst bleeding the coolant and after about 10 minutes the abs light came on so now im back to square one. it could be some more dirt on the sensor but im not sure, or could it be ive got air into the abs unit when replacing the brake lines? ive fully bled the brakes several times and can't get any air out but there culd be some trapped in the various valves within the abs unit. the brakes themselves work quite well but the abs is very easy to set off without having to stamp right on the brakes so im sure something isn't right but not sure on what step to take next.

cheers
chris

Edited by Pugugly on 15/05/2008 at 21:22

Reply | Report as offensive | Link
Thu 15 May 2008 21:41
89 3.5 535 Sport ABS Issue - Screwloose
Chris

So the light came on before the car had moved? That rules out signal errors from rust etc.

That system is too early to pick up any pressure differences caused by air; so I'd go for a sensor resistance fault triggered by suspension movement during the repairs as the most likely cause. They get fragile as they age.

Also check the charging voltage; the 2S can be a bit sensitive.
Reply | Report as offensive | Link
Fri 16 May 2008 14:10
89 3.5 535 Sport ABS Issue - thomp1983
i think it's possible i could of damaged one of the rear sensors as i had to remove it completely, or i could just not have plugged it back together 100% ill give it a good check over again this weekend and clean everything up with contact cleaner.

my main issue though is why it seems so easy to set the abs off?

chris
Reply | Report as offensive | Link
Fri 16 May 2008 14:35
89 3.5 535 Sport ABS Issue - Screwloose
Chris

Often there's no visible damage; as the sensor and it wiring age, just a change is stress can be enough.

A marginal signal from a sensor could be making the ECU think that a wheel has locked under braking.
Reply | Report as offensive | Link
Fri 16 May 2008 14:49
89 3.5 535 Sport ABS Issue - Collos25
Short them out one by one .
Reply | Report as offensive | Link
Fri 16 May 2008 14:56
89 3.5 535 Sport ABS Issue - thomp1983
i presume you mean as in remove the sensor connector and put a piece of wire across the connector? if so why, and what would i be looking for happening?

chris
Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide

If you cover no more than 100 miles per day and have easy access to a charging point at home or work, then an EV is ideal for you.

Is an electric car right for me?