Porsche Enthusiasts Club Forum

Hi All.

Please allow me to tell you my tale of ABS woh and ask for your help!

Previously my 944 had an ABS fault whereby I start engine and all warning lights go off as normal.

I start driving and when the abs system does it’s self-test the ‘!’ Light and anti lock light come on, accompanied by the noise under bonnet so it was obviously failing this test.

So I had a mate come round and help me start trying to sort.

Could not hear anything clicking on the pump relay etc.

We checked the fuses in the under-bonnet fuse box and these were fine.

My mate tried jumping terminals 30 and 87 on the ABS relay in fuse box with no change.

I’ve removed the abs ecu and tested the ohm’s to each sensor ( all just over 1000) and have tested the rotational voltage and each is registering a speed related voltage at the pins when I spin the wheel. All ok.

Here’s where things go wrong!
I thought I would double check everything from scratch and I found that my mate thought he jumped terminals 87 and 30 on ABS relay but had actually branched 87 and 15.

I have refitted the ABS relay and now I can hear the relay on the back of the pump clicking but instead of the ABS and antilock lights disappearing on start up they are now on permanently!

So..
1 – what damage could have been done by the shorting of 30 and 15 on fuse box?
2 – what next other than some sort of mental breakdown?

Thanks so much in advance
Steve

Hi Steve

Your original symptoms suggest a wheel sensor issue (sensor or wiring to sensor), as that would normally put the lights on about 5 mph when you pull off, same time as the pump self tests and you hear it whirring.

You current symptoms would suggest the ABS ECU (or a relay) has possibly been damaged by your wire jumping, causing immediate lights on, on ignition.

There is an earth wire for each sensor as well, these quite often can corrode and the wire detaches from the ring terminal.

However, I am no expert and it could be something else. My next move would be trying to borrow or acquire a known good ABS ECU to plug in, and see if you are back to square one?

Stuart

Cheers Stuart.
All the sensors test out fine.
I've done a bit more testing and ended up whipping the front wing off to access the pump.
Looks like previous owner had had issues with the pump as the two relays on top were brand new.
I've put 12v directly to the pump motor and it sounds horrendous so I'm pretty sure I've found the culprit and will be looking to either find a good used pump or someone to rebuild it if possible.

Thanks

Steve

No worries. I'm sure the part cross references to a W124 Mercedes that can be used with very minor mods and is so much cheaper.

I got a decent 2nd hand one from the states a few years back (before I was aware of the Merc pump), I figured getting a used one from a warm, dry place would be a better option, so far so good.

My fault was different. Pump was seized internally, but the ECU did not know this, so I got no lights on at start up, and no lights on at the 5mph self test, just simply if I needed the ABS, it didn't work! Anyway, replacement pump cured it.

Good luck, looks like you might be on to something!

Cheers

Stuart

All sorted now.

I didn't want to get into a rebuild myself so whilst I am aware of the merc pump, that wasn't for me.

If anyone needs a pump rebuilding then JMG in Dorset do it for a reasonable cost and have access to all the Bosch parts.

My problem turned out to be a faulty ECU.

Thanks Stuart for the advice. appreciated.

Regards

Steve

stuart

no earths on the ABS sensors, they are a closed loop system, the earth is for the brake pad warning lights

Aha! Every day a school day. Confusing for an amateur sleuth like myself with an earth on each end of the ABS loom. Very sneaky from Porsche.....

And welcome back Martin!