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Another P38 ABS brake issue

Discussion in 'Range Rover' started by ThatchP38, Oct 11, 2021.

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  1. ThatchP38

    ThatchP38 Member

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

    2002 Range Rover P38 LHD.
    Here 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.
     
  2. Rubberknees

    Rubberknees Well-Known Member Full Member

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    Can you smell any burning in the fuse box, they have been known to have problems
    Oh and welcome by the way. Help will be on its way
     
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  3. tomcat59alan

    tomcat59alan Well-Known Member

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    You say you have checked all fuses and relays, what's the fuse box like? Any smell of burning? Welcome by the way.;)
     
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  4. ThatchP38

    ThatchP38 Member

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    Thanks.
    Nothing burning but I did find a melted blower fan relay when I bought it. The brakes seemed to be working fine regardless.
    That's another issue I'm working on.

    I can't see how it would be related but this all happened right after I cleaned the maf sensor and the plug with electronic cleaner because I got a maf sensor code. That actually has gone away.
     
  5. Rubberknees

    Rubberknees Well-Known Member Full Member

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    Copy cat:D
     
  6. tomcat59alan

    tomcat59alan Well-Known Member

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    Ooop's I must have been typing when you posted, great minds or fools seldom differ.;):D:D
     
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  7. Rubberknees

    Rubberknees Well-Known Member Full Member

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    We could be telepathetic:rolleyes::D
     
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  8. RangeRoller dt

    RangeRoller dt Well-Sprung Member

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    ask Brian about setting the plunger thing or check searchbar
     
  9. ThatchP38

    ThatchP38 Member

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    Does anyone know the proper procedure for testing the pressure switch?
    I have mine plus two used ones but one is from a 1994 Jaguar which I doubt would work anyway. A definitive test if anyone knows how to do that would be great before I search for another part.
     
  10. brianp38dse

    brianp38dse Well-Known Member

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    Was the ecu changed for the correct one,the late cars with 4 wheel traction control use a different ecu which is very pricey compared with the others
    the abs tc lights will only go out after the car has moved above 5mph and checked the system,
    there is a switch on the brake peddle which needs setting, you hold peddle down, pull plunger out then let peddle back up
    if you have not yet downloaded Rave the official workshop manual do so it is a must for p38 owners
    if you bleed the brakes it must be done to the letter of the instructions in Rave.
     
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  11. Datatek

    Datatek Well-Known Member

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    The pump relay is known to fail, and as others have the fuse box may be toast especially as you had a melted blower relay.
    the pressure switch is also known to fail but to have a failed pressure switch on 2 pumps is unlikely and as the pump runs when the relay is jumped I think you can rule that out.
    I would have the fuse box out, split it and look for damage.
     
  12. ThatchP38

    ThatchP38 Member

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    ABS ECU was swapped with an older one, I think a '99 car.

    The spare switch I got is used and was part of a whole brake pump unit from ebay.
    I ordered another new old stock switch that has never been used hoping it works or at least rule that out.
    I took out the fuse box and couldn't find any damage to it.

    The is a really nice vehicle and drives great.
    I decided I was I for a penny, in for a pound, and am going to get all systems operating correctly
     
    Last edited: Oct 14, 2021
  13. ThatchP38

    ThatchP38 Member

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    Update:
    No luck so far. Found another used pressure switch no change.
    I did put power directly to the black/yellow wire in the plug and it energized the relay and pump turned on.
    It would not turn the pump on if I put power to the black/yellow wire (from the back if the plug) if it was plugged in to the switch.
    There is continuity between B/Y, B/W, and one of the ground wires. Not sure if this is correct or not.
    There is also continuity among all wires from the pressure switch plug to the corresponding wires in the ABS ECU plug (middle black one)

    I can't figure out where the fault is. Anyone have any thoughts? I've tried another used ABS ECU, from an older P38 and no difference.

    Please help!!!!!
     
  14. Mark Piercy

    Mark Piercy Well fumbled member.... Full Member

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    Trapped in moi ouse.....
    Hmmm, if you have swapped out various parts at the brake end and still have no joy then go backward from there, power supplies, fuse box (closer inspection).. Have you been over all the wire connections to the pump and switch.
     
  15. kermit_rr

    kermit_rr Green Member Full Member

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    P1592 is off road signal implausible. I get this on mine, and I think is related to a bad wheel sensor output.
     
  16. ThatchP38

    ThatchP38 Member

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    I have checked the wires to the pump and switch and the pump will power on and I can get the ABS relay to kick on with power to the black/yellow wire.
    I haven't messed with the wheel sensors yet. Do you think a faulty wheel sensor could cause the brake pump not to come on?
     
  17. kermit_rr

    kermit_rr Green Member Full Member

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    Wheel sensor shouldn't impact, but the black relay will
     
  18. ThatchP38

    ThatchP38 Member

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    Thanks. The relay kicks on and pump runs when I apply power directly to the black/yellow wire at the plug for the pressure switch.

    I've tried two other pressure switches (used) and I suppose with the age of these cars it possible that all of them are bad. I'm doubtful but it's possible.
    I have arriving today or tomorrow a brand new old stock switch that wasn't cheap but I need to eliminate the switch as the issue ( or solve the problem)
     
  19. Datatek

    Datatek Well-Known Member

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    The black relay is a known failure item.
     
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  20. Scotiawhiskers

    Scotiawhiskers Well-Known Member

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    RAVE may give you issues running on W10 - you need to set the .exe to open in compatibility mode for XP ideally to get it working.
    It is full of info, plus there is lots on here and lots of helpers too. Wiring diagrams in RAVE are a nightmare to follow though, could be written in Klingon!
     
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