FUEL PUMP ALWAYS ON

Scwhitten · Jun 6, 2026

Ok, so you know when you turn the key to ON you hear fuel pump come on for a few seconds then shut off (at least I think that's what's supposed to happen)? Well when I turn the key to ON, I hear it, but it doesn't stop. Even after the car has started, I can still hear it from several feet way. Can anybody help me with this? The pump is new. I know people might want to jump right on that and say it came bad from the factory, but I just don't believe that is the case.

Thank you.....Scott
2001 Mustang GT
Only owner.

Scwhitten · Jun 6, 2026

Scwhitten said:
Ok, so you know when you turn the key to ON you hear fuel pump come on for a few seconds then shut off (at least I think that's what's supposed to happen)? Well when I turn the key to ON, I hear it, but it doesn't stop. Even after the car has started, I can still hear it from several feet way. Can anybody help me with this? The pump is new. I know people might want to jump right on that and say it came bad from the factory, but I just don't believe that is the case.

Thank you.....Scott
2001 Mustang GT
Only owner.

I will add that the tank is on Empty, there is enough gas to start it, but it's basically empty. Not sure if that matters.

nickyb · Jun 6, 2026

New or old pump shouldn't matter, full or empty either way the ecu sends power the pump to prime then shuts it till the engine is running.
Your constant running is somewhere in the wires ,ecu, relay?

Scwhitten · Jun 6, 2026

nickyb said:
New or old pump shouldn't matter, full or empty either way the ecu sends power the pump to prime then shuts it till the engine is running.
Your constant running is somewhere in the wires ,ecu, relay?

Yes, thank you for responding. The fuse is fine. I looked for the relay but my Chilton's doesn't talk about it other than showing it in the wiring diagram for the whole electrical system. YouTube says it is in the same box as the fuse but in my car, it is not. There are 5 relays in my fuse box (under the hood adjacent to the battery), none of them are the fuel pump relay, according to the owners manual that came with the car.

Would you know where it is In my car, 01 GT? I saw something about a relay behind the glove box, but I didn't think it was my model car.

Thanx again nickyb.

Mcmahst · Jun 6, 2026

Try this:

1994-2004 SN95 & New Edge Mustang Fuel Pump Relay Location

A big issue that many SN95 and New Edge Mustang owners have is finding their fuel pump relay location. So, we at LMR have provided a quick location guide.

lmr.com

Scwhitten · Jun 6, 2026

Mcmahst said:
Try this:

1994-2004 SN95 & New Edge Mustang Fuel Pump Relay Location

A big issue that many SN95 and New Edge Mustang owners have is finding their fuel pump relay location. So, we at LMR have provided a quick location guide.

lmr.com

Seriously? Why would they put in there, in a hidden box, sealed with rivets, then soldered to circuit board??? Great!!!!

So under the video, it says..."Most fuel pumps emit a low-pitched hum or whine that can be detected from within the car if you listen carefully or from the outside of the car, close to the fuel tank. When the fuel pump relay malfunctions, power will be cut off, rendering the pump inoperable and silent when the ignition is turned on." My problem is that fuel pump is only silenced with the key is in the OFF position.

So, not the relay?

Thanx Mcmahst for your response...

Mcmahst · Jun 6, 2026

IDK, but you can probably test voltages from the box to determine if power is constant to the pump. Now, I’m not any kind of knowledgeable person on these years of Mustangs. You’ll need someone who knows the diagnosis steps to deal with this. Also, have you checked for codes? Most of the time, we skip that critical step. Good luck.

Mustang5L5 · Jun 7, 2026

There isn’t a relay. Theres a fuel pump module in the trunk on the drivers side. Gets signal from the ECU.

Either a module issue or ECU issue here.

Scwhitten · Jun 8, 2026

There is a relay in the CRMM which is hidden nicely underneath the front right fender, but people say they have never seen that go bad. I don't see the crmm in your diagram, are you sure that's a diagram for a 01 GT?

Scwhitten · Jun 8, 2026

Mcmahst said:
IDK, but you can probably test voltages from the box to determine if power is constant to the pump. Now, I’m not any kind of knowledgeable person on these years of Mustangs. You’ll need someone who knows the diagnosis steps to deal with this. Also, have you checked for codes? Most of the time, we skip that critical step. Good luck.

I know there's constant power to the pump because as soon as I turn the key, the pump comes on, and stays on after car starts up. I would love to see a very good drawing/schematic of the system....

Mcmahst · Jun 8, 2026

Did you tell us engine/trans combo?

Mcmahst · Jun 8, 2026

Also, a few pics of the top of the engine so we can see what’s what. What I’m wondering is, does your fuel rail have a pressure transducer on it to measure the fuel pressure at the injectors? Again, no expert, if you can verify that, it might help. Also, did you run for codes? They are very useful for diagnosing. Good luck.

Cartel · Jun 15, 2026

the relay could have "welded" contacts making it stay on

nickyb · Jun 15, 2026

Sometimes its the loose nut behind the wheel.

Scwhitten · Jun 30, 2026

Cartel said:
the relay could have "welded" contacts making it stay on

Wouldn't the pump stay on even with the key in the off position or not even in the ignition?

Scwhitten · Jul 1, 2026

Mcmahst said:
IDK, but you can probably test voltages from the box to determine if power is constant to the pump. Now, I’m not any kind of knowledgeable person on these years of Mustangs. You’ll need someone who knows the diagnosis steps to deal with this. Also, have you checked for codes? Most of the time, we skip that critical step. Good luck.

P0193 Fuel rail pressure high. I already tried the old one that I switched it out cuz of a different problem. It didn't fix that problem either.

Mcmahst · Jul 1, 2026

Do you know if there is a code for the pressure transducer itself or the fuel pump driver module (FPDM) For what it’s worth, I suspect the FPDM is bad, but it would be great if there was a code for that. Good luck.

Scwhitten · Jul 1, 2026

Mcmahst said:
Mcmahst said:

I don’t even think I have a FP transducer. I know I have a FP sensor and a FP regulator but I haven’t seen any mention of a FP transducer. I have a brand new Fuel Pump. I’m going to plug it in and see if anything changes. At least if I plug it in and nothing changes then I’ll know the new pump that I put in is not bad from the factory.

Click to expand...

Do you know if there is a code for the pressure transducer itself or the fuel pump driver module (FPDM) For what it’s worth, I suspect the FPDM is bad, but it would be great if there was a code for that. Good luck.

Mcmahst · Jul 1, 2026

Your fuel pressure rail sensor has likely failed; why you have the code. Here is a helpful guide to resolving this code:

Ford P0193 Code: What It Means and How to Fix It

Your Ford's check engine light just came on, and your scanner pulled a P0193 code. Now your engine's stumbling, barely starts, or just died at a stoplight. This post breaks down exactly what's happening, why

cartipsdaily.com

It’s either the rail sensor or a wiring problem. I hope it’s the sensor because wiring problems are no fun. Good luck.

Scwhitten · Jul 2, 2026

Mcmahst said:
Your fuel pressure rail sensor has likely failed; why you have the code. Here is a helpful guide to resolving this code:

Ford P0193 Code: What It Means and How to Fix It

Your Ford's check engine light just came on, and your scanner pulled a P0193 code. Now your engine's stumbling, barely starts, or just died at a stoplight. This post breaks down exactly what's happening, why

cartipsdaily.com

It’s either the rail sensor or a wiring problem. I hope it’s the sensor because wiring problems are no fun. Good luck.

Great article Mcmahst, thank you. What struct me was the empty fuel tank section. After replacing the fuel pump and fuel tank, I only put enough gas in it to start the engine. So, maybe there isn't enough gas in the tank. So I'm off to fill my 5 ga tank and come home and start putting gas in. Funny thing is, I asked about the no fuel in tank thing and somebody said it didn't matter. Fingers crossed. Thanx again Mcmahst...

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