I will be as concise as possible in outlining the history behind my question.

The vehicle was out of service for about 2 months, during that time the rear wheel bearings and brake pads were replaced and the front wheel bearings pads, tie rod assembly, lower ball joints and pads were replaced. All sensors and hubs were checked for damage and cleaned, all wiring connections were double checked for security.

Upon putting the vehicle back into service all systems indicated clear via the instrument panel. The brake pedal felt soft with the engine off and also when the engine was initially started. At the time I attributed this to the initial repositioning of the brake pistons with the new pads.

While exiting the gravel drive the triangular ASR indicator came on as expected when the rear wheel spun, on the next application of the brakes the BAS, ASR, and ABS indicators came on and have been on since. The ASR warning lamp does not come on when the rear wheels spin and there are no rear wheel brakes. (Both rear wheels spin freely on a grass surface while holding the brakes on and bringing the RPM above 1500 while in drive)

The Bentely manual suggest that low battery voltage could cause triggering of the indicator lights. The negative battery cable was lifted and the battery charged at 15 amps, it took 2 hours to get the battery to full charge. The cable was reconnected and the vehicle started and driven but the indicators are still on and the rear brakes not working.

Under traditional pre-ABS diagnosis I would replace the master cylinder, no rear brakes, spongy pedal, brakes pump up some but still don't work on the rear. I am not knowledgeable enough with regard to the exact workings of the ABS system to know if an error in it would prevent engagement of the rear brakes. If I had a suitable pressure gauge and fittings I would check the master cylinder at its discharge ports.

My questions are: Is the master cylinder a prime suspect here and if it is bypassing in the rear section will the installation of a new cylinder restore the functioning of the BAS ASR and ABS and turn off the fault indicators?
Can any ABS faults be located with an OBDII reader or are they all in the domain of the factory tool?

Sorry for the length of the post.

T W Hudson
hpshooter@juno.com