So I did a fast, high speed stop the other day in the 740 and had all four wheels lock up. This vehicle has ABS (the pump/solenoid unit is in teh engine bay).
What is my first step in diagnosing this problem? Can I pull codes out of the diagnostic terminal on teh strut tower for ABS?
I am assuming the ABS light on teh dash has been tampered with, as it does not light up on pre start. Will the ABS light tell me anything other than it is not working? It does not flash codes?

Regards, Andrew.

 

The self diagnostic unit does fuel and ignition systemsonly.

The ABS light should come up on pre-start and go out if the system is working properly. If it fails to go out or comes on at any other time it is telling you there is a problem.

It is possible to test parts of the system with a multimeter, but first check the fuse which is under the instrument panel near the steering column.

 

O.K, I have run the full diagnostics on teh car, the transient surge relay came up bad, so it has been replaced with a new one. The ABS ECU earth seemed to be suspect according to teh multimeter, does anyone know where the ECU earths? I did not try very hard to trace the wires, I was running out of time.
However, I still have the ABS light constantly on.
Will the ABS ECU reset after running diagnistics at start, or does it hve to be reset to clear the light?
Will the brake light warning module affect the ABS system? Mine is constantly on due to running LED bulbs.

Regards, Andrew.

 

Way up under the dash on the drivers side there is a relay with a fuse make sure the fuse isn't blown.

 

It's not, it is also a brand new relay......

Regards, Andrew.

 

Strange. The fuse should be part of the relay.

 

I should have said it's not blown. As I have typed, it could heve been misunderstod as the fuse is not part of the relay. It is. The fuse is not blown and it is a new relay.

Regards, Andrew.

 

Then I would look at the sensors.

 

All sensors, power supplies, earths and ancilliary equipment on the ABS system has been thoroughly checked and tested O.K. for voltages, resistances etc.
I have done all the tests, including the bridging the ABS ECU terminals to excite the ABS pump and relay etc, as per the scans of the manuals online (all 16 pages of testing).
I even went out and rechecked every earth in the car today, plus hit them with waterproof grease to ensure they stay good. They're all excellent.
The light is constantly on from key to ignition to shutting the car down. The light does not even flicker at any stage of vehicle operation.
It's very frustrating as there is no indication of any failure anywhere....
*edit, this is a 1990 model 740 turbo wagon, Australian delivered(I doubt that matters, Volvl were a global car). It is the update model. Photo here:
Regards, Andrew.

 

Sorry man not sure what to say from here. The car doesn't havea diag. system but to keep the light on when there is a problem.

 

I am considering trying to borrow another ABS ECU, it seems to be that teh computer must be the issue here, as everything else checks out.
The ECU lights the ABS light, and nothing else is failed in the ABS system.
I haven't come across a "dud ECU" issue online, so do not know if it is common or not.

Regards, Andrew.

 

I have never seen it before either.

 

Sounds like it's time for a new ABS module.

 

Could you e-mail me those pages for the ABS diagnostics please

Thanks David