AJM PD lift pump, no power at harness?

[Ryder1032]

Hey everyone. Having trouble with the lift pump on my 1999 Bora AJM TDI. Drove the car in the shop for floor work about a month ago, got ready to bring it out and now there’s no power at the lift pump harness. I had the fuel lines disconnected at the back of the passenger floor and had unplugged the harness so it wouldn’t pump fuel if I had the key on (added a sub amp with the carpet out and wanted to test it.) That was all I did to the fuel system and electrical.

I pulled the harness and tested for any voltage or signal while turning the key and got nothing. Put pins through the back of the harness and tested again with it plugged in and no difference. But, when I run a ground out of the harness and a lead off the sub amp constant 12v to the pump, it powers on so pump is fine.

After finding this out I found a detailed guide in here about testing them but after following that it didn’t lead me anywhere. I had checked fuse #28 and it was fine. I went to check the fuse in spot #10 and it seems that this car doesn’t have it. I can’t seem to find any wiring diagrams for this car regarding the fuel system either to see where the relay would be located or just to follow the harness. The only relays under the dash I have are:

Spot #1 relay #79
Spot #9 relay #53
Spot #12 relay #109

I’m absolutely stumped on what to do next but start pulling my interior again and tear apart the wiring loom and follow it to wherever it goes. If anyone can point me in a better direction id appreciate any help or advice.

 

[Vince Waldon]

To clarify, are you missing ground or +12V at the pump?

 

[Ryder1032]

To clarify, are you missing ground or +12V at the pump?

I’m missing +12v at the pump. Sorry for the scramble haha.

I figured out that the 4wd golf/Boras have their fuel pump relay in spot #9 instead of 10, and I mistakenly read it as relay #103 underneath it, but spot #9 is actually relay #53. (I will correct my first post).

Testing the relay plug I found these were the connections:
Pin 30: +12v constant
Pin 85: +12v switched to key
Pin 86: +12v switched to key
Pin 87: Lift pump +12v

On the relay plug if i jump pins #30 and #87, I get power to my lift pump and it comes on with the harness plugged in.

What could cause it to not switch on with the key with the relay in? I swapped the pump relay with my 04 golf and the golf pump powered on like normal but still nothing with the golf relay in the Bora.

Would anyone have a wiring diagram of a BEW lift pump or any other PD that i could try and go off?

 

[Ryder1032]

So I’ve been playing around with it more, I took a good relay and made a wire harness with spade connectors to clip onto the relay and plug into the relay socket to test voltage at the relay pins with it still getting direct power from the relay socket. With everything plugged in, I get a constant 12v at the relay, and with the key turned 12v to both switched pins, but nothing at 12v to the pump. To make sure the relay was fine, I put the 12v constant and 1 switched lead directly on the positive battery terminal, and testing for voltage at the switched end for the pump everything checks out normally with the fuse and it works as it should.

I had also put a jumper wire in the relay socket from one of the switched 12v sockets to the lift pump socket and turning the key wouldn’t do anything, but jumping it from the constant 12v turned the pump on instantly.

So why is it that jumping constant 12v to the lift pump main power in the relay socket will send power to the pump, but jumping from switched 12v and turning the key on doesn’t do anything although putting out the same voltage? I’m really not at all an electrician or very good with electrical issues so I’m not too sure where else to look. I’ve got to stop by vw tomorrow so I will be picking up a spare relay for the few dollars it costs and trying it out but I don’t think that’ll make a difference.

 

[KrashDH]

You say 85 and 86 are both switched to the key 12V?

That's not how a relay trigger works. One needs to be switched 12v and the other needs to be ground.

Then the coil is energized in the relay and completes the connection between 30 and 87 and sends power to the load.

So it makes sense if both 85 and 86 are hot so that when you turn the key on, nothing is happening since you're not completing that circuit (no ground) but when you jump 30 and 87 your pump works, since you're physically making that connection happen rather than it being done by the relay's energized coil.

 

[BobnOH]

Could this simply be a bad wire/connect? Test the wire from pin 87 to the pump.

 

[Ryder1032]

You say 85 and 86 are both switched to the key 12V?

That's not how a relay trigger works. One needs to be switched 12v and the other needs to be ground.

Then the coil is energized in the relay and completes the connection between 30 and 87 and sends power to the load.

So it makes sense if both 85 and 86 are hot so that when you turn the key on, nothing is happening since you're not completing that circuit (no ground) but when you jump 30 and 87 your pump works, since you're physically making that connection happen rather than it being done by the relay's energized coil.

Ahhh okay i see what you mean. So if everything is sending correctly throughout the relay and working properly except for power out to the pump on the relay, there’s no ground to complete the relay. Is the ground wire pin #4 on the lift pump harness the only ground wire for the pump wiring? and jumping 12v to it from pins 30 to 87 I’ll get 12v at the lift pump harness testing pins 1 and 4.

 

[KrashDH]

Ahhh okay i see what you mean. So if everything is sending correctly throughout the relay and working properly except for power out to the pump on the relay, there’s no ground to complete the relay. Is the ground wire pin #4 on the lift pump harness the only ground wire for the pump wiring? and jumping 12v to it from pins 30 to 87 I’ll get 12v at the lift pump harness testing pins 1 and 4.

No what I'm saying is either pin 85 or 86 on the relay needs to be grounded to send power THROUGH the relay to the pump when the key is turned on. If you jumped pins 87 and 30 manually, and your pump turned on, it means your relay is physically working and your pump is grounded properly.

Look at a diagram online of a typical 4 pin relay. 85 and 86 pins need to complete a powered circuit (key on) which magnetizes a coil internal to the relay. In order to complete a circuit you need a path which means you need power (from the switch) and a ground.

When that coil is magnetizes, it physically "pulls" a jumper connection from 30 to 87 so voltage and current can flow through it.

 

[BobnOH]

I will look for a wire diagram for a PD, I may have one.

 

[BobnOH]

Wire diagram for early PD

 

[Ryder1032]

Thank you both for the help and guidance, really set me in the right direction and that pd wiring diagram was a huge help.

Been going over the wiring diagrams for the lift pump and here’s what I seem to understand about the relay:

Pin #30 is a constant 12v, and when the circuit between pins #85 and #86 is completed, it delivers power to the lift pump pin #87. Pin #85 is a the ground for the circuit controlled directly by the ecu when the key turns on. Pin #86 is a switched 12v, which is the completed circuit of relay 109 when the key is turned on.

I went to test the relay socket after better understanding how a relay works and seeing the wiring diagram. With the key off, a test light clamped to the positive 12v of a battery and probe touching pin #85, the test light comes on. Testing with a multimeter, touching negative to pin #85 and positive to pin #30, I got just over 12v. Touching negative to pin #85 and positive to #86, was about .2v, showing no positive signal with key off.

Turning the key on, testing with a voltmeter at pin #85 for ground and pin #86 for a switched 12v showed no signal and continued to show no signal switching key on. Grounding the multimeter pin to the ground under the steering column and touching positive to pin #86 showed around 12v with the key on and would shut off with the key off.

So overall, I have constant 12v at pin #30, switched 12v to pin #86 with key on, but I only get a ground to pin #85 with the key off. So the ground pin #85 is turning off with the key on, and back on with the key off. Therefore the circuit between pins #85 and #86 cannot be completed and will not allow pin #30 to send power to the lift pump pin #87, because there is no ground signal to pin #85 with the key on.

In the wiring diagram it shows that pin #85 is directly wired from the ecu with the exception of a connector through the rain tray into the interior. If it shows a solid ground and no issues with the key off, then there should be no issues with breaks in the wire etc. If the only thing that wire leads to is the ecu, would this be my culprit? That’s what’s it’s starting to seem like. Pin #85 seems to be the problematic one. Thanks again to the both of you for the guidance and help.