Porsche Enthusiasts Club Forum

I have just bought my beautiful 1987 944 (non-turbo) and I'm delighted with it apart from the fact that the ABS light has gone from intermittent to ON solid. I know this topic has been discussed before in the forum but maybe someone can point me in the right direction with some tests I can do to ascertain where the fault lies without it costing me a fortune at the Porsche dealers. I have been working on all sorts of cars for a long time (too long!) now and know what I'm doing. I have checked the wiring from the 4 wheel sensors and found one chaffed wire (sorted I thought! Wrong) and cleaned 8 barrel shaped connector blocks (2 on each wheel) all seem clean and in good contact.
* Is there a simple way of checking the functioning of the wheel sensors? I was wondering if I connected a bulb and 12V across the terminals would that be sufficient if I spun the wheel to indicate the pulsing of the sensor was operating correctly?
* Are there any other simple tests I can do on the ABS relay? I know where it is in the fuse/relay box but it won't pull out! Does it have something actually holding it in? I don't want to just yank it out and break the mounting.
* Any other tests I can do with a multimeter?
Thanks for your help.

This happened on my 928 and the simple test I conducted was, does it come on before you move? If so its the ABS pump. The sensors don't come into action until you reach 5 mph I think? This might be the case on the 944?

The relay should just pull out of the fusebox.

Does the ABS light go out after the engine is started and then come on when you move?

Does the ABS light go out and stay out until you get past 5mph (as lee said)?

Does the ABS light not go out when the engine has started?

Answers to these questions should narrow down the causes.

Ideally you should test an ABS sensor by spinning a wheel with the sensor connected to an oscilloscope. But if you hook a multi meter to one, set it to volts AC (important to be AC) and spin a wheel, you should see a small AC voltage.

You can also test the resistance of the sensor, all 4 should be roughly the same within 200 ohms, but from memory I think they are usually around 900 ohms, but I would have to check.

Thanks for the replies. This was exactly what I wanted. The ABS light is ON from when I put the ignition ON and never changes so I'll check out the pump. The ECU, just by my right knee, if I can read it correctly actually says '928' on it

I had problems with my ABS which started out as light coming on sometimes after reaching 5mph.It then went to condition of always on and no pump noise when self testing when just driving off .
In the end went through the whole system

sensors where all ok and as Jon says norm is 900 ohm when spun.
earths were badly corroded and the earthing wires in the barrel connectors were shot with age and corrosion - ended up replacing all barrel connetors to be sure - not cheap re: £90 each from Germany
once knew all that was ok I replaced ECU with a known Bosch engineer checked one , still problem so my ECU was ok
Then went for the pump - siezed solid , probably by age , conditions where it is mounted and other problems with earths not allowing the pump to self test - lack of use = siezure.

I have a spare fully tested ECU and front and rear sensors if you find you need them.

Good luck

Nick

[color=#000080]Thanks for all this very helpful advice particularly Nick and Jon. I have this morning got access to the ABS pump and the rest of the electrics behind the right hand front wheel and it is, as you suggested, horribly corroded and the earth was just about hanging on. I remade the earth hoping that was the problem. No such luck! As I need the car over the next few days I wasn't going to start stripping the whole unit out with all the implications for the brake bleeding etc., but just one question...noting your comment about the pump self testing, when I turn on the ignition should the pump make a noise? Does it run all the time or only on demand? Just thought it might help with the diagnostics. Thanks for the offer of the ECU I may take you up on the offer sometime.
Thanks again
Norman

Thanks for all the information Jon. I have joined the club. Shame you are so far away (I live near Blackpool!) But we do have friends down in Bournemouth so if I can't solve the ABS problem you may be getting a visit!
Norman

Hi this was the case on my S4/928 same as Lee 944 post.light on all the time . cleaned all connections and then found out it was faulty relay. to test you can jump two connections where relay plugs in can not remember which two but when jumped A/B/S works .

if everything is working well when you set off the ABS pump self tests and you should here a short whirring sound from the o/s front.

Nick

JMG does set out a good procedure on how to check them.

When a sensor died on my 106 GTi a couple of years ago, I found the iffy sensor by checking all of the resistance values with a multimeter.

Thanks for all the advice re the ABS problem. Having checked all the wheel sensors (each about 900 ohms) I decided I had to tackle the relay in the fuse/relay box. This relay was in solid! I was worried about pulling it out in case I wrecked part of the box but needs must...Eventually got it out, tested it and you've guessed it..it had failed! Got a relay from a right-off (£26 from Porscha-Recycled) and the ABS now works perfectly! Result!

As you say, result.

Hello, Ive recently encountered the same problem of ABS light permanently on.

Ive checked the sensors, im getting just under 1k Ω , this means the earth strap works no ? because if it didnt, it wouldnt give a signal no ?

The abs relay works, the fuses i think 19 and 26 are fine.

Im coming to the conclusion that the abs ecu is knackered, im going to check that there is power supply to the box. I imagine there must be to get the fault light in dash no ?

Ive heard the abs pump upon disconnecting the connector plug to the ECU whilst the car is running , (which you are not supposed to do), so I dont think the pump is seized.

Has anyone got any ideas for me please...... Thanks in anticipation.


1989 944 lux 2.7 Guards Red 74k

im currently trying to sort out an abs issue on my 2.7 .

My mechanic told me it was the o/s rear that was the issue so i took it out and replaced it . Image below the what the old old looked like when i took it out .....

Its no wonder it wasnt working. The problem remains however . Same as before the abs light goes out as it should but then comes back on soon after you start rolling.

I have cleaned off the old sensor as i suspect it was all the crap on there that led it to malfunction .I have also attempted to remove the n/s rear to see if that was the issue but it is stuck fast iin there . Any ideas how to get it out hopefully without having to pull it apart.

If it comes on when you move def a sensor issue

And for those with a seized pump buy one for a 190 merc and swap the motor and pistons

Cheap fix, even the relays in the merc pump are the same