DSC/ABS lights with codes 51 and OE (valve relay fault)

[goinstrong]

I have a '98 740i with the newer ABS/DSC setup (precharge pump next to the master cylinder). The brakes are currently semi locked "on". I can move the car, but it takes a bit...no coasting at all, and the front tires don't rotate when lifted off the ground. I replaced all 4 wheel sensors, disconnected the ABS module, but it didn't change anything.

I suspect the ABS module, but am wondering if it might be that DSC precharge pump that has gone bad. When I clear the codes, I can hear the relay clicking, but nothing happens. I am not sure if the ABS module is sending the signal, or if it goes the other way.

Any thoughts on where to go from here? Thanks!

Tim

Additional question: I haven't pulled all the fuses for the ABS/DSC system. If the brakes pop loose, does that confirm the module and or pump? If not, does it mean the Master cylinder is bad? Thanks!

[BMtroulbewe]

Try jumping the relay and see if you can hear the pump engage.

[Timm]

Disconnect the loom from the ABS/DSC unit - that should turn all the valves OFF and release the brakes. But, I've never heard of this happening before - but I have heard of the master cylinder causing this problem, so my money is on the master cylinder!

[goinstrong]

I did disconnect the loom from the ABS/DSC unit, but the brakes didn't release. I thought they would as well. If I touch the brakes, they still activate, but actually grab when BARELY touched. Maybe it is because they are already partially activated. Your point about the master cylinder is a good one, unfortunately! It will be next week before I can get to it, but I will update.

Could a bad pressure sensor cause the brakes to be locked up? It is a lot simpler to check/replace than the master cylinder. Thanks.
Tim

[Timm]

It's very unlikely - with the ABS/DSC disconnected the sensors/motors/valves are de-activated and it reverts to a simple brake system - and the only thing that causes the brakes to lock is the master cylinder.

[goinstrong]

Thank you for your guidance. It is truly appreciated. I will update the post after I have a chance to replace the master cylinder...hopefully that it solved the problem!
Tim

[goinstrong]

UPDATE: With a suggestion from my sons, I had my wife apply the brakes, and I cracked the brake line from the master to the precharge pump. A burst of air, then fluid, and the pedal went to the floor. After tightening it up, topping off the fluid, the brakes work much better. I will still bleed them.
BUT...the DSC light flashes on any acceleration. I push the DSC light so it stays on, and the car functions perfectly. Is one of the new wheel sensors bad? Any simple way to tell? I will update again after bleeding the brakes. Thanks!
Tim

[Timm]

Check the tyre sizes axle-to-axle, and the tyre pressures. If the rear tyres rotate faster that the fronts you will get this problem.