[Moose Test]

Hi Iain,

I don't know of a *simple* way to reliably verify the actual operation of the valve. It is actuated by means of a simple solenoid coil so it would be possible and prudent to test it electrically to start with. I'd remove the electronic module in the foot well and with reference to the wiring diagram for your model year, locate the two blade receptacles in the module's socket which run to the control valve.

In my case (MY 2007), these were terminals 1 and 5 (with yellow and brown wires running from them, respectively).

A multimeter on its resistance range should read somewhere between 7-15 (-ish) ohms if the coil is intact. If you read open circuit then you've either a wiring fault (bad connection, broken wiring etc.), or the coil has burnt out. If you see a short circuit then again, you've a either a wiring fault (most likely) or the coil has burnt in such a way that it's windings are fused.

Even if the coil is intact, that is not to say that the mechanical action of the valve is ok and it could still be at fault.

I'd be very carful about applying 12v directly to the coil as, depending on what's actually going on, you could end up burning the supply wiring. At least, ensure that you don't do it directly from the battery without some kind of fusing in the circuit (2 or 5 amp fuse would be appropriate). I've seen the post that you refer to and whilst I see the logic in it, I don't think that this method really proves definitively that the valve is working within expected norms. The electronic module near the pedals is actually a digitally controlled constant current source and in normal operation, limits current flow to the valve (who's fluid response is proportional to current, not voltage) to no more than 1 amp. Just wiring the valve's coil to an unlimited current source proves nothing - if it opens fully with 5 amps applied (i.e. it's sticking) what then? It clearly is still faulty and won't work correctly with the range of current being applied by a functional electronic control module.

That said, with the appropriate precautions, it would prove that the pump is supplying sufficient pressure and that the rack is mechanically sound.

I think the ideal test of valve operation would be to use a current limited power supply powered from the car battery. That way, you could set and limit the amount of drive applied to the fluid valve and test that it responds accordingly whilst driving the vehicle (with an assistant, of course).

That's a lot to be going on with, so I'll summarise by saying that I would check the resistance of the coil first (from the control module socket), to eliminate wiring problems and other, obvious failures. If all is ok (around 7 to 15 ohm resistance on the coil) then apply 12v to it but do so with a fuse in the circuit (5 amp max, 2 amp min). If it works then, it possibly is the module at fault. If it doesn't, then it's the valve, pump, or rack.

BTW - if it does prove to be the valve, this can be 'replaced' using a Volvo supplied repair kit, rather than having to replace the entire rack.