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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Sun, Jan-19-2020, 02:57:08 PM   #1
M spec
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Default Fuel pump relay shorting out (grounding issue?)

After extensive head banging, I have found that somehow the fuel pump relay is shorting out (didnít blow the fuse in the front of the car)

My assumption is that thereís a bad ground somewhere, that or somehow the pump is all of a sudden drawing too much power? But Iíd assume if that happened the fuse would blow.

Iím at a loss of where the grounds would even be. Could other systems grounds be affecting it? Say the alarm systems?

When I had the CSL roof down there were a few grounds that didnít look like they were installed back in the rear c pillar. I guess I should start there.


However wondering if anyone has any insight or suggestions as to why Iíve blown through 4 relays in 48hrs
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Old Sun, Jan-19-2020, 04:21:40 PM   #2
bigjae1976
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Default Fuel pump relay shorting out (grounding issue?)

I believe the relay ground is under the rear deck right near the relay.

Thereís 2 wires that run to the relay. One to the fuse box and one to the DME box. If you plug another relay in and the relay goes bad, Iíd suspect that the issue is between the relay and the fuel pump. Might be a pinched wire somewhere? Or maybe the fuel pump is shorted out. Or the pump is causing an overload (impellers jammed up with debris?) which burns up the relay.

Iíd resistance test the ground wires and then resistance test the positive wire between the fuel pump and relay. If both are good, Iíd think it points to a bad pump.


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Old Sun, Jan-19-2020, 05:10:22 PM   #3
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Default Re: Fuel pump relay shorting out (grounding issue?)

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Originally Posted by bigjae1976 View Post
I believe the relay ground is under the rear deck right near the relay.

Thereís 2 wires that run to the relay. One to the fuse box and one to the DME box. If you plug another relay in and the relay goes bad, Iíd suspect that the issue is between the relay and the fuel pump. Might be a pinched wire somewhere? Or maybe the fuel pump is shorted out. Or the pump is causing an overload (impellers jammed up with debris?) which burns up the relay.

Iíd resistance test the ground wires and then resistance test the positive wire between the fuel pump and relay. If both are good, Iíd think it points to a bad pump.


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Appreciate the post. I think Iím going to pull this pump, for the 9th time in the last 6 months.

Not sure the Radium engineering kit is all that great
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Old Sun, Jan-19-2020, 07:28:44 PM   #4
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Default Re: Fuel pump relay shorting out (grounding issue?)

Another thing to look at is the ignition coil ground on passenger side of engine. If that is not grounded properly it will back feed and kill fuel pump relay.


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Old Mon, Jan-20-2020, 02:54:44 AM   #5
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Default Re: Fuel pump relay shorting out (grounding issue?)

A bad (shorted to ground) pump should cause fuse blown instead of fried relay. Same with a pinched wire from relay to pump.

This is a semiconductor relay and a bad ground on the relay can fry it. Just measure the ground pin to chassis to check.
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Old Mon, Jan-20-2020, 02:55:23 AM   #6
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Default Re: Fuel pump relay shorting out (grounding issue?)

A bad (shorted to ground) pump should cause fuse blown instead of fried relay. Same with a pinched wire from relay to pump.

This is a semiconductor relay and a bad ground on the relay can fry it. Just measure the ground pin to chassis to check.
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Old Mon, Jan-20-2020, 04:41:10 PM   #7
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Default Fuel pump relay shorting out (grounding issue?)

Okay new update..

Went to my local dealer 100 miles away. Bought 4 new relays, swapped in a fresh one. Drove around PHX and then back home 100 miles. Probably started and turned the car back on 3 times?

Yesterday morning went to a start the car and nothing. Dead. Replaced with a new relay. Nothing. Checked grounds. All tight. No clue how to check for a pinched wire.. but from what I can see the wires look fine. 5 hours later I tried again to start the car. Turns right over..


I then had an idea to swap in one of the ďold relaysĒ fired right up.. Iím at a loss. And I feel ****ed. Iíve spent about 3-4hrs in diagnostics. And you have to drive it around too recreate the stalling. A shop will insist on doing the checks Iíve done (as they should IMO) and still be where Iím at. This might be the one time I wish I hadnít DIYíd and taken the car to a great shop.


Going to try to get the pump warrantied. Thatís the last piece that would make sense.

Last edited by M spec; Mon, Jan-20-2020 at 05:10:55 PM.
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Old Mon, Jan-20-2020, 07:29:56 PM   #8
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Default Re: Fuel pump relay shorting out (grounding issue?)

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Originally Posted by M spec View Post
Yesterday morning went to a start the car and nothing. Dead. Replaced with a new relay. Nothing. Checked grounds. All tight. No clue how to check for a pinched wire.. but from what I can see the wires look fine. 5 hours later I tried again to start the car. Turns right over..
Don't panic -- it is an easy to find out which part is the root cause. I don't think relay is the problem.

The relay 9-pin connector: whenever the problem happens, measure voltage at pin2 which should be 12V when pump suppose to run. If not 12V then measure the relay control input at pin4 which I think should be 0V when active and higher voltage when not active (you can verify this when engine is running). Also measure pin6 and pin8 which should have 12V with key turned on.

If pin2 has 12v and pump not running then either a bad pump or the wire between pin2 and pump is open or bad connection. Use a light bulb connect to pin2 and ground and if the light turns on then relay is good. Then check the switched voltage at the pump. If it's 12v then bad pump. If not 12v then wire has bad connection.

Last edited by sapote; Mon, Jan-20-2020 at 07:33:51 PM.
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Old Wed, Jan-22-2020, 06:28:50 PM   #9
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Default Re: Fuel pump relay shorting out (grounding issue?)

I had a similar, very funky and erratic, problem that I thought was relay related when I had an aftermarket pump. I went back to the OE pump.... Never an issue since. And never had to mess with the relays again.
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Old Wed, Jan-22-2020, 06:40:50 PM   #10
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Default Re: Fuel pump relay shorting out (grounding issue?)

YA I was gonna say earlier, $20 you pop an OE pump in, even a used one, and all problems will go away.
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Discussing Fuel pump relay shorting out (grounding issue?) in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)