Porsche Enthusiasts Club Forum

Hi all,

How can I work out where the problem lies?

Cheers, James

Describe how the lights comes on, the sequence.

Start engine, no light. As soon as I move 10-15 metres I get ABS light and the warning triangle show on the dash. This will stay there until I switch of the ignition and will appear again once the car has rolled 10-15 metres.

James

Nice to know I'm not the only one .... same here but I've ignored it so far.

G

When the ignition is switched on the ABS light on the dash should illuminate.
When the engine is started the light should extinguish
When the car reaches 3-5 MPH the system should carry out a sensor and valve check sometimes a noise can be heard from the front OS wheel arch.

If the ABS light stays on after engine start there could be a few reasons for this.

1. Brake light Switch Fault
2. ABS pump Relays
3. ABS relay G20 (944) G22 (968)
4. The ABS ECU Grounds
5. The ABS Wheel Sensor Grounds
6. The ABS Pump Ground
7. The ABS ECU

If the light goes out with engine start, then comes on when reaching 3-5 MPH this is caused by a malfunctioning wheel sensor, ground or the sensor.

Wheels sensors will only provide output to an oscilloscope for full diagnosis but it is possible to test them with a DVM.
When the hub is spun as fast as you can by hand (direction does not matter) the sensor should output a very small voltage AC, they should all be about the same output, for the same spin speed.

Checking the resistance will only show they are not open circuit.

Checks
1. Make sure the toothed section on the rear of the hubs is free from rust and metallic particles and dirt.
2. Make sure the head of the sensor is also clean and free of dirt.
3. Check cable continuity for the ABS sensor cables.

If one sensor puts out a significantly lower voltage than the rest replace it

The ABS sensors can be tested at the ECU cable connection.

Right Front ECU Plug Pins 21 and 11
Front Left ECU Plug Pins 6 and 4
Rear Right ECU Plug Pins 24 and 26
Rear Left ECU Plug Pins 8 and 9



If you have no warning light after moving off and no ABS, I would suggest that the ABS pump is seized in the valve block and needs replacing.

if anyone has any more information or tests that would help please add them in

Pins for the ABS Relay

Pin 15 Is the voltage sensor from the Altenator

ABS ECU Information

Two ABS ECU's can be used in our cars but don't be fooled by the part numbers, I have had this checked out by OPC in Polaris which is their parts history system.

The ECU that appears on eBay most often
928 618 119 05
This ECU was used between 1984 and 1991 for 928,944,944S2

928 618 118 00 is the later ECU fitted to 968, later 928
This is the correct one for our cars but both will work

The later ECU is now only available as an exchange part at the paltry sum of £744.00 plus £200 parts deposit plus VAT


Abs Pumps Modulators that can be cannibalised for parts.

Porsche 944S2, 968 Standard Abs Modulator
Bosch Pump 0265 200 038

Donor Pumps
Bosch Pump 0265 200 043 Mercedes W124 Chassis from 190 to 500SL
Bosch Pump 0265 200 042 BMW All sorts

hope this helps

Thanks Martin,

I dont have an ABS issue... yet... but this is genius! Thanks in advance

Great write up Waylander!
I have a question now, I have no abs lights up or brake fault lights on my 944s2, I hear the test function when moving off, does this mean that the abs is functioning correctly?
Or is there other tests to ensure.
I don't want to start slamming brakes on etc.
By its very nature its dormant until needed.
any thoughts.

Mark

Find some grass to test it on at about 10mph that saves damaging your tyres

I would recommend doing this frequently to stop the pump siezing up as alot will be doing at 25yrs old plus.
The pump sits in a potential rot box area !
Nick

Thanks for this info. I'll have to investigate further when I get some time. Hopefully next week.

James

Hi all,
thanks for the excellent advice. Could someone help me out with the ABS testing a bit more as I'm uncertain on a couple of bits.

I have an ABS light permanently on (although once under heavy breaking it went off for a second a few weeks ago).
I've taken out the ECU and tested all the sensors from there and checked the sensors themselves visually. Also tested the relay and tried a replacement one.

What I'd like to do now is diagnose the problem to either the ECU, wiring harness or the abs pump itself.
I don't know how to test this exactly. According the guide above, I can test the pump by applying 12v to the ABS ECU and terminal 87 in the fuse box.
How do I do this? I have a 12v test probe so I can only supply 12v to one at a time. Also, unsure where to find terminal 87, assume it is one of the connections when I remove the relay itself.

I'm not too good at electrical fault testing as you can tell, so any advice is extremely welcome.

if you turn the key to position 2 all the dash lights should come on this is a visual check, then when you start the engine the ABS light should go out.

If it does not then you have a fault with the ECU or the earth on the pump or the relays on the top of the pump.

I need to remove that part about 12v in terminal 87

thank you waylander.

How can I rule out the ECU or the pump now? (I have a 944 turbo by the way)
I ahve a 12v test probe and a multimeter at my disposal.

I have tested all the ABS sensors but as you say I start the car and it stays on its the pump or the ecu most likely.
I'd like to rule out one or the other next but I don't know where to start.

I read somewhere I can put a wire between two slots in the relay in the fuse box and that will turn the pump on. Is there a way of achieving the same result with my 12v test probe?

Update to my diagnostics testing:

1/ Checked the power at the terminals in the fuse box 12v across the desired terminals
2/ Relay works perfectly and clicks
3/ If i close the circuit manually across 30 and 87 (like closing the relay) the abs pump relay clicks

Interestingly when I started the car the abs flickered off for a split second but its still on permanently.
I've cleaned the terminals in the fuse box and checked the wiring to the ECU last night.

Where is the ground on the ABS pump, do I need to take off the plastic wheel arch guard and inspect the pump?
I can find a spare ECU for £25, but I want to see if I can narrow it down first. I assume I can do this if I can get the pump to run manually?

If so, how can i test the pump, assume if I supply power to one of the ECU terminals I can send power to the pump, but I'm not sure even after looking at the wiring diagram.

Thanks again!
Austin

One sure way to test the pump is to apply power to the big red power lead that is on the rear of the pump but of course you can't see this as its buried in the off side wheel arch, you need to get the arch liner off and you will see what I'm on about.

No room to move can't see what your doing, I ended up in my checking and testing releasing the bottom of the wing and taking the three bolts out of the wing to A pillar joint then I could see the rear of the pump.


The earth is at the front of the pump so that's easy, a jump lead is big enough to put the current needed through the pump.

The abs ecu is an easy swap, on the 968 it's in the drivers footwell by your right knee, needs a like acrobatics to get at, I would borrow one to test with