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Discussion Starter #1
Hi Everyone, I'm a new member here with a bit of a fuel pump dilema.

I'm working on my cousins 2006 G6 3.5L V6.

Car would crank but not start, couldn't hear the pump, Checked and no power at the pump. Replaced blown fuse and then had 12v on the Gray wire to the pump. Yet the pump would still not kick on.

Put in a used (not my idea) pump and still the pump does not turn on. I can jump both pumps directly to the battery with a couple of jumper wires and both of them turn on.

I still have 12v back to the pump along with a good ground. There is no visual damage to the plug or harness.

This one is really baffling me.
 

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the only thing that I would think of off hand is a possible issue with the wire from the fuses to the pump...since you've tested and know the pump works if you bypass and jump straight from the battery. but, I'm no expert
 

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Hi Everyone, I'm a new member here with a bit of a fuel pump dilema.

I'm working on my cousins 2006 G6 3.5L V6.

Car would crank but not start, couldn't hear the pump, Checked and no power at the pump. Replaced blown fuse and then had 12v on the Gray wire to the pump. Yet the pump would still not kick on.

Put in a used (not my idea) pump and still the pump does not turn on. I can jump both pumps directly to the battery with a couple of jumper wires and both of them turn on.

I still have 12v back to the pump along with a good ground. There is no visual damage to the plug or harness.

This one is really baffling me.
So the pump is not activated at all at KeyOn? Not even for a second or two? Have you swapped the pump relay out?
 

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Discussion Starter #4
Nope, The voltage pops up with key on but the pump will not run. I've tried in the tank and out of the tank with no results.

Only way I've been able to get it to run is to take the pump and jump it to the battery with short jumper wires.
 

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Nope, The voltage pops up with key on but the pump will not run. I've tried in the tank and out of the tank with no results.

Only way I've been able to get it to run is to take the pump and jump it to the battery with short jumper wires.
So you have a steady B+ out of the relay on the grey wire into the pump & the black ground checks out yet two pumps won't go hot?
 

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Discussion Starter #6
So you have a steady B+ out of the relay on the grey wire into the pump & the black ground checks out yet two pumps won't go hot? I don't see how that's possible.
I don't either, That's why I'm quite confused.

Only thing that is bothering me is that the second pump is used from a less than reputable salvage yard. They had already purchased the pump and then asked me to install it.
 

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I don't either, That's why I'm quite confused.

Only thing that is bothering me is that the second pump is used from a less than reputable salvage yard. They had already purchased the pump and then asked me to install it.
But you tested both pumps with B+ directly & they activate so I think you covered that. Since pump fuse 25 was blown at the onset, I have to suspect a harness issue. Yet you say that has checked out too. Is there fuel in the tank? Maybe the pump has an automatic cutoff (unsure). You have checked the ground for high resistance? You are using a multimeter & not a continuity checker.
 

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Discussion Starter #9
But you tested both pumps with B+ directly & they activate so I think you covered that.
Yeah, I just can't figure out what the difference is between me feeding it 12v directly off the battery and the PCM sending it the 12v through the harness.

I am using thick gauge house wire to jump from the battery, maybe that is allowing for more amperage to flow to the pumps? IDK, I'm reaching at straws now..
 

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Discussion Starter #11
12 volts doesn't mean much, will it light a high amp bulb. If not poor connection, no amperage.
I just went and load tested the circuit with an old 75w off road light and it lights bright. Also did a continuity test on the gray power wire and black ground all the way from the fuse box to the tank and they checked out good.
 

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I just went and load tested the circuit with an old 75w off road light and it lights bright. Also did a continuity test on the gray power wire and black ground all the way from the fuse box to the tank and they checked out good.
Continuity is not very helpful. You can have good continuity & very high resistance simultaneously.
 

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I have not worked on these circuits in a long time but GM used to switch all their computer controlled circuits except fuel pump by supplying constant ignition voltage and switching the ground side. The fuel pump at that time (early 90's) was switched 12v for safety. If you are able to light the lamp on the gray wire anytime the ignition is on then they switched to controlling the fuel pump by switching ground on and off. The up shot is a bad connection at the PCM or heaven forbid the blown fuse event took out the power transistor in the PCM, the power transistor is supposed to be protected but may not always work. YMMV as I have not looked at a wiring diagram for this vintage car yet, I just finally moved out of the 1990's by buying this 2009 G6.
 

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Discussion Starter #15
In the G6 there is a constant ground, when the ignition is turned on the PCM send power to the relay which then allows power to the pump for 2 - 3 seconds to prime it and then shuts off power if the computer does not detect ignition. So it's still about the same as the 90's.

Both of the vehicles I own are from the 90's too, much easier to work on. lol.
 

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Discussion Starter #17
I'm very curious to find out how this turns out.
Well, I got it fixxed today. Turns out I was getting continuity to ground through the B+ wire running from the Relay to the tank. I cut out the old wire and patched in a new one.

I'm still not really sure how I was able to power that 75w off road light on the circuit without blowing the fuse. So I'm not sure how I was getting the readings I was getting. Wiring is not my specialty.

But the car runs good now, so my cousin is happy to have her car back.
 

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Discussion Starter #19
Sounds to be like you're pretty good at it. A voltage drop test would have shown that B+ short to ground. Now I'm kicking myself for not suggesting it.
I appreciate you coming back with the conclusion. Probably won't be the last time this problem occurs with that harness.
Yeah, I wouldn't doubt it. Kinda seems like once one electrical problem arises, more are sure to follow.
 

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I wanted to post this in case someone needs it in future fuel pump circuit troubleshooting:

Fuel pump diagnosis: Electrical tests
Replacing an electric fuel pump on a modern fuel injected vehicle is not a job to be taken lightly. In this and two follow-up articles, we'll cover the basics of electric fuel pump diagnosis, to help you increase the odds of diagnostic success when you suspect fuel pump problems. We want you to be absolutely certain that a fuel pump replacement is required before you remove the old one. We'll begin with electrical diagnosis.

When the ignition key is turned to the ON position, you may be able to hear the PCM turn the fuel pump on briefly. For safety reasons, the PCM will turn the pump off again in a few seconds if the engine doesn't start. When the ignition key is moved to the START position and back to ON, the PCM relies on the crank position sensor to determine whether the engine is running.

Let's assume you didn't hear the pump run when you turned the ignition on. There could be at least three reasons why it's not running:

* For some reason, the PCM has decided not to turn on the pump.

* There's a fault in the circuit between the PCM and the pump.

* The pump really is shot and nothing's going to make it run.

We'll eliminate two obvious choices right off the bat and assume the PCM is commanding the fuel pump relay to turn on and power the fuel pump. And we'll assume the pump is in good shape, too. Something between the PCM and the fuel pump is keeping the pump from operating property.

Attach a digital multimeter (DMM) to the positive and negative fuel pump terminals, then turn the ignition on. Your DMM should briefly read battery voltage. If it doesn't, look for a break in the circuit somewhere between the fuel pump and the relay. The relay itself may also be defective.

If the pump is receiving power and ground, determine whether it's receiving enough of both. Due to its low impedance, your DMM may indicate battery voltage at the pump. But a voltage drop test may reveal that something less than battery voltage is actually reaching the pump when the circuit is loaded.

To voltage drop test the entire fuel pump circuit, begin by dividing the circuit in half-the ground side of the circuit first, then the positive side. All tests must be conducted with the circuit "live." Use a fused jumper wire to energize the fuel pump relay and power the pump circuit.

With the circuit energized, connect one of your DMM test leads to the negative battery terminal and the other to the negative terminal at the fuel pump. If the ground circuit is in good condition, your DMM should indicate a voltage drop of about .1 volt or less. Anything greater indicates an unacceptable amount of voltage is being lost before it reaches the pump. Damaged or corroded wiring or harness connectors are most likely responsible.

If the ground side of the circuit checks out, with an acceptable voltage drop, repeat the voltage drop test on the positive side of the circuit. Back probe the output terminal on the fuel pump relay with one DMM probe, then the positive fuel pump terminal with the other probe. If the DMM indicates a voltage drop greater than .1 volt, find the damaged harness connector or Airing that's responsible for the drop.

Use the "split half" method to determine where the faulty wiring is located. Divide the circuit in half, then repeat the voltage drop test between the middle of the circuit and the relay, and between the middle of the circuit and fuel pump. This allows you to determine whether the fault exists in the front or rear half of the circuit. If the drop is greater in the rear half of the circuit, divide the circuit in half again and repeat the split half test. Each time you divide the circuit in half, you'll be one step closer to finding the fault.

Remember, no fuel pump can be expected to operate properly on reduced supply voltage.
 
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