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2013-2015 Range Rover Sport
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158 Posts
Discussion Starter #1
About a week ago my ABS pump started to fail. This presented itself as the red brake light on the cluster while driving. I could get it to work buy pulling the plug, reseating again, and the pump would work long enough to turn the light out. I decided it was time to further investigate and ultimately just decided to get a good P38 pump and do the swap.

No issues with the swap except there’s now no power to the pump. Fuses are good. Relays are good, i think it will confirm once I can get them tested. When a put a voltmeter to the new plug I have zero volts to the plug. When I pull the relays I have >13v coming to relay #2, but only .30v to relay #3. I’m sure I’m over complicating and probably conflating all kinds of other things, but basically I need help troubleshooting the problem and fixing it.

BL: There’s no power to the new pump and I can’t figure out why

Thanks in advance!



283006
 

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1970-1995 Range Rover Classic
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102 Posts
First, you could try running the pump straight from the battery using a couple of wires to make sure you got a good pump.

There are a couple of spots where power to the pump is cut off. The pressure switch and the abs relay. You could use jumper wires and make it so the pump runs and then work your way through the circuit.

That Falconworks abs PDF book is great resource on figuring out how the system works and troubleshooting problems.
 

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2013-2015 Range Rover Sport
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158 Posts
Discussion Starter #3
Thanks! I’ve had success jumping relay #3, and decided to jump a ground from the white with orange dots, which turns the pump on and the brake light off. Now the pump will not stop running even though the brake light is off. I’m really close to by passing it all and just wire a toggle switch when needed.
 

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1970-1995 Range Rover Classic
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102 Posts
First off, wiring in a toggle switch to essentially turn on and off your brakes is how you turn your Rover into a death trap.

Second, if you hot wired #3 of course the pump isn't going to shut off. The brake light going out just means it's gotten to the pressure needed to turn off the light, that's not the same pressure as needed to shut off the pump. It sounds like you've thrown too many variables into the mix. If pulling the #3 relay and plugging it back in fixed your problem temporarily then the problem was the relay, not the pump. But now that you've thrown in an unknown pump you could actually be looking at multiple problems.

This is how I would go about troubleshooting, with the goal of getting the pump to work properly (as in it runs for <60 seconds before shutting off, turned on after pressing the brake pedal 3-5 times and then turned off)

1) test that the pump turns on by hot wiring the plug, only do it briefly, just want the make sure it turns on, if it doesn't your electric motor is dead.
2) test the wiring to the abs relay (#3). First make sure at the relay plug that the pump turns on with a jumper wire, again only run it briefly. If it doesn't work, then you have a problem with the wiring to the pump (or a blown fuse).
3) Plug the abs relay in, and then unplug the pressure switch plug. On the plug you can short the right two wires (the top and bottom) and that should turn the pump on. If it doesn't, there's an issue with the wiring or the relay failed open. If the pump runs without you shorting the pressure switch plug, then the abs relay failed closed. You need to replace it.
4) Check if the pressure switch works, first, check that there is continuity on the switch by using a multimeter on the left two pins on the switch (top and bottom). Then plug the plug back into the switch and turn the ignition on, the pump should turn on. If you don't have continuity or the pump doesn't turn on, the pressure switch is bad.
5) Make sure the pump and accumulator are bled properly. Then turn the ignition on, the pump should not run for more than 45-50 seconds before shutting off. If it doesn't you could have air or gunk in the pump.
6) if the pump shuts off properly, pump the brakes 4-5 times, the pump shouldn't kick on before pressing the brakes at least 3 times. It should also take more than a few seconds to shut off again. If the pump only runs for a couple of seconds and/or it only takes 1-2 brake presses to kick on the pump, you have a bad accumulator.

I'm sure I glossed over something, but that should be the basic roadmap for testing it. It sounds like your original problem was just the relay was on its last leg. If I was doing the testing, I'd put the old pump back in place to cut down on variables, but that's up to you.

Whatever you do, don't put a toggle switch in for the abs pump. I don't know if you were joking, but for the sake of posterity and anyone reading this, it's a horrible idea. If you are sick of the abs pump system then put in a master cylinder and vacuum brake booster from a Discovery 1 or pre-ABS Range Rover. Make sure you check the diagrams for those systems and you hook everything up properly (proportioning valve in the right spot and the brake lines going to the right spots).

Brakes are not something to half-ass.
 

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2013-2015 Range Rover Sport
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158 Posts
Discussion Starter #5
Happy to report that the problem was traced back tot the pressure switch. Put in a new one and now it works as advertised.
 
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