So I know a lot had been written in the ANS issues with the Range Rover p38 and I have read everything I can find and am still stumped.

2002 Range Rover P38 LHDHere is a list of my symptoms and everything I have tried...

Car running great, no brake issues, occasionally abs brake and TC lights would flash on and off when first pulling away then didn't come on.

Put it in garage to do some cleaning and check code which was for maf sensor. Removed it, sprayed with electronic cleaner and replaced, also sprayed plug connectors.

After a while doing some cleaning of the rest of the inside, I started it up and immediately had ABS, brake and TC lights on and soft pedal, no braking power, but would build some pressure back with multiple pumps of the pedal but braking quality still poor.

Checked codes and no more maf sensor code but got p01592.

Not much other history because I purchased the car a week before this.

So I began diagnosis...

Checked and rechecked all fuses and relays, no issues.
Brake pump will not turn on unless I jump the relay, then braking power returns but ABS and TC lights remain on.

Replaced accumulator with new one, no change.
Replaced entire brake pump unit with used, no change.
Tried to test/ground pressure switch with no results. Tried to ground the black/yellow wire in pressure switch and pump did not come on on either unit.
Cannot seem to get power to the plug for pressure switch. I've tested each pin and nothing. Not sure if there is supposed to be power but seems likely.
Have continuity on pressure switch (both)

Replaced ABS ECU with a used on, no change.

My conclusion is that the relay is not getting the signal to turn the pressure switch on but I cannot figure out why. And my test of the pressure switch and plug are inconclusive in my opinion.

Could a faulty wheel sensor cause all this? I didn't think that it would cause the brake pump to not come on but I'm not sure.

Sorry for the long explanation but wanted to put as much information as possible.

Hopefully someone has some ideas or other ways of improving my diagnosis techniques.

 

Wow, you’ve done a lot of work already. I haven’t really had brake issues with mine so no experience to draw from. Presumably you tried a different relay (in the location that you jumpered to make the pump run). Otherwise I think you’re correct about the relay not getting the signal to close its contact. I actually had that relay fail on (pump kept running after turning car off). You could also try posting in the P38 part of this forum, you might get someone who’s had this same issue.