WABCO C ABS - Disco1 and RR Classic

[joe1]

Been trying to resolve this problem for a few days now but getting bogged down largely I think because I lack understanding of how the system is supposed to work, so time for some additional input I think before I drive myself deeper into a bottomless can of worms (and desparations!). I've posted here because similar systems are in both D1 and RRC.  

Background: D1 300tdi 1996 auto - new to me, abs dash bulb had been removed (nice) and initial error code shown was 2-6. Easy I thought so changed brake light switch, clearing the error, and promptly got the new code 2-2. According to the RSW solutions site this code means

“1. Pump relay doesn't switch off or 2.Wiring Connection 'Pump Monitor' to ECU”

I've gone through a number of checks on the power supplies, relay operations, ecu connections and continuities, and everything seems to check out apart from what follows.

1. The pump relay – does not run the pump when ignition is on brake pedal is depressed (**check my understanding here – should ignition on and brake pedal pressed be enough to run the pump??**). But if relay terminals 85 and 86 are bridged the pump runs. Power supply on NO to the relay is ok at 12v. Relay when tested out of circuit latches ok on a 12v supply. When the relay is removed from circuit and put back it still doesn't operate - the problem seems to be that WO from ecu terminal 11 has only 0.1v – not nearly enough to trigger the relay. Presumably on receipt of 12v from the brake light switch terminal 11 should have a bigger output voltage? So does this mean the ecu is faulted or is there another condition that isnt being met?

I've done similar checks for the Load relay – supply on OK is good, but the BG output from terminal 8 of ecu is 0volts, so again this relay is not operating in circuit.

2. Pump monitor to ecu. This is terminal 30 on the ecu. I presume terminal 30 is waiting for 12v from NR on the pump relay. It doesn't receive 12v because the relay doesn't operate.

This all seems pretty much self defeating unless I'm missing something blindingly obvious. An thoughts/inputs welcome. I've extracted some wiring schemes attached for the relevant bits mentioned above. Cheers.

[elbekko]

10 hours ago, joe1 said:

the problem seems to be that WO from ecu terminal 11 has only 0.1v

Did you verify this at the ECU or at the relay? Could always be a problem in the wiring there.

As for actual operation, not sure, I only know the P38 system and there the pump starts running if the pressure is low and the ignition is on. The pressure switch is definitely worth checking if the pump doesn't do anything.

[joe1]

3 hours ago, elbekko said:

Did you verify this at the ECU or at the relay? Could always be a problem in the wiring there.

Yes, I checked both. In fact interestingly that cable showed no continuity from ecu to relay - so I replaced most of it with new cable. Your point though does now make me think that I might not have re-checked the voltage back at the ecu terminal after the replacement wiring. I'll do that later today and report back

 

3 hours ago, elbekko said:

As for actual operation, not sure, I only know the P38 system and there the pump starts running if the pressure is low and the ignition is on. The pressure switch is definitely worth checking if the pump doesn't do anything.

I think the details are different with the D1 - there is no accumulator on these and so no pressure switch. That ecu terminal instead has a second feed from the brake light switch (which also showed 12v at the ecu with brake pedal depressed). So its a simpler system (but still unfathomable to me!).