ABS pump failing over and over and over!!!
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Thread: ABS pump failing over and over and over!!!

  1. #1
    FRESHMAN ROVER
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    ABS pump failing over and over and over!!!

    My old 1999 P38, which I sold keeps burning up ABS pumps. I believe this is the 5th pump its burned up in the past year. Something is causing it to stick on. The ABS pumps have all been BRAND NEW pump/accumulator/switch assemblys. We have replaced the relays a couple times, put in a new fuse box and changed out the brake booster....same results.
    We did however find that the guys who installed the aftermarket navigation system tapped in to the ABS harness near the computer to get the speed pulse signal. We removed that wire but this issue happened once again. We are 100% stumped at this point. Yes the brakes are being bled properly (no air bubble noises, etc) and yes the fluid has been completely flushed to ensure it is not contaminated. The first pump was replaced about 8 months ago and it lasted about 3 months with no problems. The second one was replaced and that lasted about 1 or 2 months, the third one lasted only a week, and the 4th only a day, the 5th one now only lasted about 30 minutes.

    This is becoming very frustrating, inconvenient and extremely expensive! Anyone with any ideas PLEASE chime in! Thanks VERY much!
    2004 Range Rover - 18" 10 Spoke Wheels - Cooper Zeon LTZ 285/60
    Past Rovers:
    1999 Range Rover 4.6
    1998 Discovery

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  3. #2
    JUNIOR ROVER
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    Re: ABS pump failing over and over and over!!!

    Ok, You have replaced the Accumulator as well as the pump, so that cannot be losing or have lost pressure.
    I assume there is no loss of fluid.
    It seems a silly question, but I'm struck by the shorter and shorter timescales between failures.
    When each pump has failed, how do you know the pump has failed? What are the symptoms or loss of performance?
    When it lasted a month, did the pump just seem to run a lot, but cut out occasionally?
    When the pump lated 30 minutes, was it running continuously for all the 30 minutes?

    Cheers.

  4. #3
    FRESHMAN ROVER
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    Re: ABS pump failing over and over and over!!!

    Quote Originally Posted by Chas
    Ok, You have replaced the Accumulator as well as the pump, so that cannot be losing or have lost pressure.
    I assume there is no loss of fluid.
    It seems a silly question, but I'm struck by the shorter and shorter timescales between failures.
    When each pump has failed, how do you know the pump has failed? What are the symptoms or loss of performance?
    When it lasted a month, did the pump just seem to run a lot, but cut out occasionally?
    When the pump lated 30 minutes, was it running continuously for all the 30 minutes?

    Cheers.
    No fluid loss. The pump no longer operates, burns up the motor itself. ABS and Brake light comes on when it fails, indicating the ABS fault and brake pressure loss. Fault stored is "stuck pressure switch" When the pump turns on and off, it always operates normally 4-5 brake pumps before it kicks on and re-pressurizes. The last time it operated, not sure. I did not drive it, but it definitely stuck on at one point and burned up.
    2004 Range Rover - 18" 10 Spoke Wheels - Cooper Zeon LTZ 285/60
    Past Rovers:
    1999 Range Rover 4.6
    1998 Discovery

  5. #4
    JUNIOR ROVER
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    Re: ABS pump failing over and over and over!!!

    OK, the Workshop Manual says :
    The ABS power unit consists of an electrically driven pump, a pressure switch and an accumulator.
    The pressure switch incorporates three electro-mechanical switches: one for the pump, another, at a different pressure setting, to illuminate the pressure warning lamp. The latter switch plus a third switch inform the ECU of low pressure and that ABS function should cease while pressure remains low.
    The pump also incorporates a non-return valve and a pressure relief valve to protect the system.
    NOTE: The pump and pressure switch are not serviceable, if failure occurs a new unit must be fitted.
    ----------------------------------------------

    So, you would think that every pressure switch could not be faulty, but something is keeping the pump going.
    As you have changed the modulator as well as the pump, we should be able to say that any dirt in the system has been flushed out with the fluid changes. Considering you have changed both the modulator and the pump the only major items left are the calipers, and any dirt in those is unlikely to get all the way back.
    Re-reading, I see you have positively said "the fluid has been completely flushed to ensure it is not contaminated. ".

    The ETM says:
    When low pressure occurs in the brake system, a switch in the pressure switch unit closes to ground the coil of the pump relay. The pump relay now energizes and applies battery voltage from the fuse to the hydraulic pump through the closed relay contacts. The hydraulic pump runs to increase pressure in the hydraulic accumulator. When sufficient pressure is developed in the system, the pressure switch opens to de–energize the pump relay and to turn off the hydraulic pump.
    -------------------------------------------
    I'm tempted to work on the principle that the relay is held operated. Can you confirm that?
    The diagram shows the signal wire from the pressure switch extends the Earth to the ABS ECU and the ABS Pump relay. In passing, I seem to recall that this relay is 'special' to handle the highly inductive and high current loading. Presumably it was changed for the correct 'special and expensive' version?
    With the wiring disconnected from the pressure switch, and the relay removed from the fuse box, check the Black/Yellow wire for earth or voltage conditions. (The other wires are Black/White and Black/Green). This is with the ignition switched on. I know the ECU is still in circuit, but a competent electrician should be able to check this wire without damaging the ECU. It's always possible that the ECU, or the plug, or the wiring to the plug, is faulty, and it's good not to disturb those items until after you have checked for the standing condition.

    With the fact that the failure time has got shorter and shorter, I'm thinking that the true fault is a wire that is failing through damaged insulation, chafing somewhere. Initially it was intermittent, but as time goes by the damage gets worse and worse so it's now full time, or practically so.
    If you do find a standing earth on the wiring, my advise is to look closely at the wiring BEFORE diving in and yanking it about, because disturbing it could destroy the evidence. Don't forget to open the plug (C0504 RHD or C1584 LHD) to look for contacts inside there.
    Also plug the wiring back into the pressure switch and examine the wiring harness for any chafing contact to the bodyshell.

    I recognise that you have changed the Fusebox, so eliminating a fault caused by that overheating etc.

    Cheers.

  6. #5
    SOLIHULL ROVER
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    Re: ABS pump failing over and over and over!!!

    Hi

    If the pump is failing due to overcurrent and it is the electromotor that gives up you have to find the cause of the overload on your pump. You need to compare current draw from a pump under normal operation in an other range rover without problems with the pump fitted to your car. If the current draw is much higher you have to search for a possible cause. The higher current draw can be caused by lower voltage which is the next thing to check how much voltage you have over the motor when in operation. It is most likely that some leak exists or that an earth point is corroded that causes a voltage drop over the earth point. The places where leaks and or voltage drops occur will usually get hot.

    The next thing is to try to run the pump straight from the power source with direct connections. If this still does not solve the problem you have to start searching at the hydraulic side to see whether anything here can cause the excess current taken up by the motor. Is the supply of oil towards the pump unrestricted? What does the pressure do? Does it go up and stay up when brakes are not operated? Does it cut off at the right pressure etc. For this last measurement you need a diagnostic system or rig up a pressure indicator into the system.

    Good luck.

    Jos
    1995 RR 4.0 SE
    Fitted with replacement engine and gearboxes from 1997 4.0 SE.

  7. #6
    FRESHMAN ROVER
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    Re: ABS pump failing over and over and over!!!

    Thanks Jos and Chas, very helpful information. I am going to print and consider what you have posted. I will let you know what I find.
    2004 Range Rover - 18" 10 Spoke Wheels - Cooper Zeon LTZ 285/60
    Past Rovers:
    1999 Range Rover 4.6
    1998 Discovery

  8. #7
    FRESHMAN ROVER
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    Re: ABS pump failing over and over and over!!!

    Ok glad I found this post. I have a very similar problem. While correcting a fault with the EAS I also decided to replace the ABS Accumulator while I was there.

    After replacing the accumulator, now the ABS pump motor runs continuously and doesn't shut off at all. Prior to replacing the accumulator, the pump motor functioned normally and would shut off when the system was pressurised.

    After a bit of fault finding and consulting the ETM I decided to replace the ABS Pump Pressure Switch. Even with the replacement switch the pump runs continually without shutting off at all. Have tested the relay and it is good. I'm now stumped and am trying to avoid the $1,650 (AUD) for a replacement ABS Pump.

    The pressure switch is not available new separately. I sourced a 2nd hand pressure switch from my local Land Rover wrecker. They pulled the switch off a broken pump unit for me for $75.

    Unfortunately I drilled a hole through my old accumulator and disposed of it so I can't use it to help with fault finding.

    So my possibilities seem to be:

    1) I could have 2 faulty pressure switches. The 2nd hand pressure switch I obtained was from a broken pump. I wasn't told what the fault with that unit was but if the pressure failed then the faulty switch won't tell the pump motor to turn off so it'll just keep running til it burned itself out. Hence broken pump. Which is exactly the same as what mine is doing. Or,

    2) Given that it only started doing this after I put in a new accumulator maybe my pump motor is dying anyway. Perhaps the commutator/brushes/bearings have worn and the pump motor is outputting less power. Less power could mean less hydraulic pressure. Maybe it's not supplying enough pressure to trip the pressure switch to tell the motor to turn off. But I'm only guessing at that and they definitely had no intention of letting anybody pull the pump motor apart once it was assembled. I thought I'd be able to pull the end cap off the motor and inspect the commutator/brushes but these motors were not designed with that in mind.

    I have bled the entire system and there are no leaks. The ABS pump functions normally during the brake-bleed procedure, except for not shutting off when it gets up to pressure. The TC/ABS lights on the dash do go out as per normal.

    This vehicle is not my daily driver so I haven't run the pump motor more than 5 mins at a time while it's in this condition. At the moment I am only running it for fault finding. Hopefully there isn't any damage to the pump motor if it isn't faulty.

    I have tried testing the pressure switches as follows. I put a multimeter across the various contacts while activating the pressure switch plunger:

    a) With the multimeter across Pins 2 & 1, actuating the plunger, the switch breaks/makes contact as per the ETM,
    b) With the multimeter across Pins 3 & 5, actuating the plunger, the switch makes/breaks contact as per the ETM,
    c) With the multimeter across Pins 1 & 4, actuating the plunger, the switch maintains a constant short circuit. Actuating the plunger does not break the circuit, even though it is supposed to.

    Both my pressure switches operate identically as above. I suspect this is probably my answer. 2 faulty switches. I do not want to lay out $1,650 for a whole pump if it is just the switch. But I have not found the switch available as a separate, new part. I may need to keep trying 2nd hand pressure switches until I find a functioning one.

    But given that etcatmeat's post above says he has burned up 5 different, brand new pumps in 12 months means I may be on the wrong track.

    Does anyone have further suggestions?
    Is allyv8 still active here?

    I'm trying to avoid burning up 5 pumps. That's a whole lotta cash I don't have.
    - Stuart
    '97 HSE 4.6 (now running LPG)
    '96 Harley-Davidson Sportster 1200 Custom

  9. #8
    JUNIOR ROVER
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    Re: ABS pump failing over and over and over!!!

    This link may help, or it may frustrate - I haven't seen in detail a Wabco ABS pump motor for either a Classic or a 38A, but this link shows the inside of a Classic version. Although not dated, the content is several years old.
    http://www.jpurnell.com/RR/repairs/abs_pump.htm

    "I haven't seen in detail a Wabco ABS pump motor for either a Classic or a 38A,"
    It strikes me that Mr Modulator Repair, also in Australia, might have seen the inside of a 38A pump (or be in a position to), and may be able to make confirmation checks on pump pressure switches. He does have proven expertise in taking complex bits apart, and putting them back together so they work

    "c) With the multimeter across Pins 1 & 4, actuating the plunger, the switch maintains a constant short circuit. Actuating the plunger does not break the circuit, even though it is supposed to."
    Haven't you answered your own question here? To the effect that the switch is jiggered (broken).
    HOWEVER - Can you recheck your pin numbers? I see your profile shows a '97 version, but I've looked at both the '97 and the '99 ETM, and neither show a design connection between pins 1 and 4. This assumes testing is done with the wiring disconnected.
    Options are 5+2, 5+4, 1+3.
    Note that the pin numbers in RAVE ETM are pins in the Connector, NOT pins on the switch - these are not numbered on the diagram, although they may be on the switch itself, but we can't see that

    You say this problem occurred since you changed the accumulator (and you have destroyed the old one), but have you carried out any sort of pressure check to show the new one is working? Or even what pressure the pump is reaching?
    Did you change the O ring when you changed the accumulator?
    I note the instruction re changing the accumulator asks you to bleed the system after the change.
    Did you do this?
    Is the problem caused because the bleeding was not effective, and that air is trapped in the system somewhere (modulator?)?

    HTH

  10. #9
    HSE
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    SOPHOMORE ROVER HSE's Avatar
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    Re: ABS pump failing over and over and over!!!

    Ok, just had time to read this thread. If a number of new components are failing in the car, it's got to be within the vehicle. If the pump is operating normally but burns out. There has to be a short or over voltage feed when the pump cuts in. Have you tried to measure the voltage at the pump when it cuts in!!!!!

    This may seem obvious, and I'm not being smart. If the pump is cycling normally but burning out fairly quickly, it has to be either a short/bad earth of over voltage spike of some kind. Very strange, I've not heard of this kind of problem before.

    I have not dis-assembled a pump before, but can if needed to help. I still believe that the issue is in the car not the pumps.
    We'll work though this there has to be a reason.

    Regards Russell.
    I'd rather push my overheated HSE than drive a tojo
    04' L322 Vogue 22' overfinch wheels
    94' Classic Vogue Plus
    93' Classic LSE
    85' Classic
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  11. #10
    SOLIHULL ROVER
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    Re: ABS pump failing over and over and over!!!

    Hi

    The brake pump from the P38 is exactly the same construction as the one in the link Chas posted. The only difference there is is the screwed on accumulator.

    It is extreemly difficult to open the electro motor and put is back together. The carbon brush holders have to be opened and kept in position while you slide the rotor back in. This is nearly impossible to achieve as the rotor is suddenly pulled back by the force of the magnet. You need to have a column drilling machine to fit the rotor in the chuck and move it down in a controlled manner while keeping the carbon brush holders in position. Motors can burn due to leaking of brake fluid towards the inside of the electromotor.

    The pump itself is easy to dismantle exactly as described in the link.

    I have not looked at the brake switch yet but I remember from the hooking up of the Rovacom that there are 2 pressure switches and also the actual pressure that you can monitor. If I have the time I will try to find the old pump housing that I have of a burned pump and look at the switch.

    Regards

    Jos
    1995 RR 4.0 SE
    Fitted with replacement engine and gearboxes from 1997 4.0 SE.

  12. #11
    SOLIHULL ROVER
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    Re: ABS pump failing over and over and over!!!

    Hi

    Did some checking of the switch and found the following:

    As Chas pointed out already there are 3 switches incorporated.

    switch No 6 with connections to pin 2 and 5 this switch is responsible for turning the pump on and off by connecting to ground.
    The other switches No4 and No 5 with connections between pins 3 and 1 and pin 4 and 5 send signals to the ECU and BECM.

    With me measuring the switch the connections are as follows.

    Holding the switch with the 3 connections at the top and the 2 connections at the bottom

    Left top is no 3
    centre top is no 4
    right top is no 2
    left bottom is no 1
    right bottom is no 5

    Without pressure no 4, no 2 and no 5 are connected together.
    With the plunger pressed in until you hear the switch click 3 and 1 are connected but also 2 and 5 remain connected. It is stated that switch 6 will only switch off at 180 bar and it might be going off when the plunger is pressed further inside. I have no tools here to test that now. The other switches are already activated at 110 bar.

    As switch 6 is providing path to earth you might want to check if there is no short from your pump or connectors towards the earth as a bypass of the switch
    as this will also cause the pump to run continiously.

    Regards

    Jos
    1995 RR 4.0 SE
    Fitted with replacement engine and gearboxes from 1997 4.0 SE.

  13. #12
    HSE
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    Re: ABS pump failing over and over and over!!!

    Just another thought, the problem is obviously a power function for the pump to run continously. This direction can only come from the abs ecu or the becm. I take it that each of the pumps have been new??? The avenue I would be taking is first of all check the wire that the sat nav unit was connected too. We all know p38's don't take kindly to having wires added to the system. Try back probing this wire to ensure that it's not broken either diection from where they added the signal wire to the sat nav.
    Not sure of the region the vehicle is from, but I find lots of harness damage causing shorts in my area due to vermin(mice rats even roaches!!!!)

    My mv system reads the current pressure of the pump it runs at about 200 to 215 bar.

    Just a word of advice, and I'm sure you would be aware of this. These pumps are designed to perform a duty cycle only. Continuous running for even twenty minutes is doing damage. There design is to cope with short bursts of a minute or so at a time. I guess what I'm saying is during testing with another pump if it has not shut off within say 2 to 3 mintues disconnect the unit and investigate. Hope this helps.

    Regards Russell.
    I'd rather push my overheated HSE than drive a tojo
    04' L322 Vogue 22' overfinch wheels
    94' Classic Vogue Plus
    93' Classic LSE
    85' Classic
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  14. #13
    SENIOR ROVER
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    Re: ABS pump failing over and over and over!!!

    Periodically on ebay rebuilt pumps with accumulators are available from an outfit in California. They ask $500 for classic or p38 pumps. Ours seems to be fine so I haven't checked into it but perhaps they are a good group and could answer some questions. If the lights go out when you drive away {to minisrangie] then it should mean that you are up to operational pressure. I have noticed with ours that if you drive off immediately after starting two of the lights stay on longer than the book says they should. {after vehicle has not been run for several hours] I believe I am overdue for an accumulator at least. Has anyone timed how long it takes or knows how long it should take for the resevoir to fill with fluid as the pressure bleeds off. I did leave info about this supplier on a post several months ago so its in the system. As you can probably tell I'm still learning how to do hyperlinks. cheers
    2004 Epson green 112k miles few records latest diff folly also 1952 Hough payloader 1959 Nuffield 4DM
    2000 kent green 4.0 SE 180,500 miles and working EAS no service records prior to 121,900 and nov 06
    2003 GMC 1500 AWD window van 5.3 L love it in the snow & rain-anytime [on mich cross-terrains] 165 plus K miles.

  15. #14
    FRESHMAN ROVER
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    Re: ABS pump failing over and over and over!!!

    After much headache and frustration we finally found the source of the problem. The infamous heater core o rings were leaking and nobody caught it! They were BARELY leaking, couldnt smell coolant or feel the carpet was wet or anything. But the drips of water were falling on wiring and running all the way to the BCM! The BCM had corrosion all over. I took the BCM apart and had it professionally cleaned and touched up the soldering. Fixed the O rings, put it all back together and its been running perfect. WOW! I'm glad that drama is over!
    2004 Range Rover - 18" 10 Spoke Wheels - Cooper Zeon LTZ 285/60
    Past Rovers:
    1999 Range Rover 4.6
    1998 Discovery

  16. #15
    HSE
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    Re: ABS pump failing over and over and over!!!

    Quote Originally Posted by etcatmeat
    After much headache and frustration we finally found the source of the problem. The infamous heater core o rings were leaking and nobody caught it! They were BARELY leaking, couldnt smell coolant or feel the carpet was wet or anything. But the drips of water were falling on wiring and running all the way to the BCM! The BCM had corrosion all over. I took the BCM apart and had it professionally cleaned and touched up the soldering. Fixed the O rings, put it all back together and its been running perfect. WOW! I'm glad that drama is over!
    Oh excellent, good out come. As I said in my posts, it had to be within the vehicle somewhere. But the matrix seals wow thats a new one for the books. Great to hear all is well.
    Regards Russell.
    I'd rather push my overheated HSE than drive a tojo
    04' L322 Vogue 22' overfinch wheels
    94' Classic Vogue Plus
    93' Classic LSE
    85' Classic
    58' 88inch series 1 "Stella"
    RX7 13b turbo 450bhp fast
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