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2 Posts
Discussion Starter · #1 ·
Story time e46 fans; it's a classic with a twist.

Cliffnotes: No ground to fuel pump relay (among other relays)

2003 BMW 325i 110k mi No mods
I've scoured the internet and cannot find an answer to my problem as the situation and issue don't match up with what I've got going on. Also, I have basic knowledge of mechanics and electronics, emphasis on BASIC.

I bought this car from a dealership about a month ago (Early Nov), no huge work needed to be done (replaced brakes and rotors, replaced 2 pullies that were screeching, and an oil change.

Fast forward to last Saturday: the car has been running flawlessly for the last month until Saturday night I suddenly lose acceleration power, which I later found out was my fuel pump dying (not totally dead yet). I can't get faster than 50 mph with pedal to the floor, but I manage to make it home another 6 miles, with decent enough acceleration and power on side streets.

I sit in my parking spot for a couple minutes and let it run, in total disbelief this happened to me (I've had horrible luck with cars in the past) and the SES light comes on. I turn the car off and listen to it die and head inside when there isn't a sound that alerts me.

I get online and research and determine it's either a fuel delivery issue or air intake issue, but I'll know more in the morning when I get an OBDII scanner to it.

Sunday morning now, I head down ready to get this problem fixed and I hop in the BMW and it cranks and cranks but doesn't start. So I pop the hood and check for obvious cracks or holes in the intake boots but they're fine. Come back later with OBDII scanner and it gives me both lean fuel mix codes, which confirms fuel delivery issue. A little more research later and I've determined it the fuel pump, but I want to be sure so I have it towed to Firestone to have it diagnosed and potentially save me some cash.

That's my backstory, sorry for the intense details, but I want to make sure I don't miss any information that could be important. Now for what I know:

FS checked BOTH fuses, and tested the fuel pump relay, all of which are good.
They checked power at the fuel pump and found that it isn't getting any power.
They did NOT check the fuel pump itself since it isn't getting power so I don't know it it's a bad pump or not.
They confirmed that the fuel pump relay and one other relay are not getting ground from the ECU/DME.

They told me they couldn't go any further in the diagnosis due to liability/equipment/knowledge restrictions, but suggested a bad ECU/DME, or bad connections/wires.

After researching similar issues I'm pretty sure my DME is good because it doesn't shoot to red temp on ignition, plus the SES light, OBDII and everything else are working.

Let me know if I can provide anymore information to help you help me!

What would possibly cause the DME to not ground the relay(s)? Camshaft position sensor, bad pump, loose/corroded/burnt up wires?

How can I test the fuel pump at home? (I have tools, but nothing fancy)

I know I may seem novice but I am awesome at following directions.

· Premium Member
28,957 Posts
Doubt your issue is the DME, could be with the key, EWS or ignition switch.

BUT, before you get to wrapped into all of this, check out the basics. Even though Firestone has looked at the car, put what they have to say aside for the moment.

2nd link below in my signature has a lot of fuel pump info.

Also understand this, the fuel pump due not have power with the key in the on position after the 5-10 second prime mode. If you measure the Voltage across the fuel pump connector after the prime cycle, you will maybe measure 5 Volts.

Suggest you make sure there is more than 1/4 tank of fuel in the car. You can use the Hidden OBC Menu to verify the fuel level in each side of the fuel tank.

See my comments in this post toward the end - http://forum.e46fanatics.com/showthread.php?t=1017077&highlight=fuel+pump

You might try measuring the power to the fuel pump while the engine is cranking, you may be able to try not to push the clutch in or try cranking the engine with the transmission is Reverse or Drive if an automatic. Not pushing the clutch in if a manual trans, or putting the automatic in Reverse or Drive will keep the engine from cranking so you can conserve the battery and possibly hear the fuel pump if it is running.

· Registered
5,239 Posts
Did they crank the engine as they check for power at the fuel pump connector?
The DME needs the signal from the CPS to power the FP.

If there is no power at the FP, the FP relay might be faulty.
Here is how you test it. Remove the glovebox to get to the relay board.
Remove the FP relay and jumper terminals 2 and 6 with a fused jumper wire.

If the pump runs, the relay is bad, if it doesn't, it's probably the pump.

You can also connect a direct lead (jumper wire) to the fuel pump, again fused wire from the battery.

BTW, welcome to the forum and to the joys of BMW ownership!

· Registered
43 Posts
I had basically the same situation like the OP have but the issue is now solved.

I have my car since new so I know how it was beatened. Long story short, I had engine cut-off many times last week and finally last Friday it cranked but refused to fire up. I checked the car, replaced the crank position sensor(the cam sensors are new) and finally identified it is the fuel pump.

You can google to find "E46 fuel pump diagnosis" and it should give you very useful information. Here is my checking to verify the fuel pump is bad or not.

Take off the back seat, on passenger side(LHD vehicle) you can find a wire goes into a cover. It is the power wire to the fuel pump. Take it out, in the socket you can find two wires sitting next to each other. One of them is the brown wire which is the ground. Use a Ohm meter to test it has a good ground. Next, with a volt meter, insert the negative probe into the brown wire socket, the +ve probe to the socket next to the brown wire.

It should read about 0V. Turn the key to run position(but not cranking the engine), you should see 12V(depending on your battery voltage) for 3-5 seconds and then it goes back to zero.

scenario 1: you see the 12 V - it most likely to say it is your fuel pump.
scenario 2: you don't - try the followings:
- check the fuse for fuel pump (#54);
- check fuel pump relay, the relay is at the back of the glove box so you need to take it out. I just swapped the fuel pump relay with the horn relay(they are identical) so the horn should be able to tell you the original fuel pump relay is good or bad;
- Fuse #3(20A) sitting in the electronic black box under the bonnet.

I did go through steps in scenario 2 because I don't see 12V initially at the fuel pump socket. I don't know why but after these steps, I re-check the voltage in the fuel pump socket, the 12V is there so I rushed out to buy a new fuel pump, replace it and the engine fires up like before.

Hope this helps.

· Registered
2016 M235i 6-spd
29,215 Posts
^ Yep...check the Kalim Fuse...the middle fuse in fuse pack--in e-box

If it's bad, it could be because on of the wires coming from one of the 9 items it feeds has a short in it. I forget which items those are exactly, but the FP relay is one of them. For me, my intake cps wire was shorted out...blowing that fuse.

If Kalim fuse is blown, you can get a re-settable fuse. Pull each item on that fuse and see whether you can get the car to go, or at least crank without that fuse blowing. One at a time. I posted list of all the items here somewhere...from Bentley. hth

· Registered
E46 F10 W204 W212
5,482 Posts
OP you may be over thinking this. The pump is a known weakness, is cheap to replace, and with those miles is a maintenance item anyway.

The power to the pump is not constant like jfoj said. Many BMW-dedicated shops will trip on the E46's eccentricities, more so a Firestone that services all makes and models.

Get it out of that shop before they charge you all sorts of diagnosis fees or worse, break it. At this point there is no savings to be had anyway because whatever you've paid/will pay them will probably be more than what BMA sells the fuel pump for, about 130 bucks delivered.

· Registered
2 Posts
Discussion Starter · #7 ·
Sorry it's been so long! Just now able to give some information and thank all of your for your responses and help.

I wish I could give individual credit to all of you but you all helped me out in a different way.

Turns all of you were right about testing everything myself; A word to the future individuals that come across this thread: Do not trust your wonderful European-engineered cars to general mechanics. Firestone must have tested the power wrong because I went back and tested it myself and read 9V (FS drained my battery :censor:) for a few seconds at key pos. 2, and again as I attempted to crank it.

I will be buying a new fuel pump and filter from BMA this evening and replacing it myself, and (hopefully) report the good news.

Thanks again to everyone who posted on this thread, and I appreciate the warm welcome to the community!

· Registered
1 Posts
Just in case anyone else has this issue in future and wants the list of items connected to each fuse relay, here you go.
  1. F1: (30A) Ignition coils-320i with MS43/325i/330i
  2. F2: (30A) Engine control module (ECM), reversing lamp/s relay, transmission control module (TCM) – 316i/318i
  3. F3: (20A) Mass airflow (MAF) sensor, crankshaft position (CKP) sensor, reversing lamp/s relay, engine coolant thermostat, camshaft position (CMP) sensor 1, camshaft position (CMP) sensor 2-320i/325i/330i
  4. F4: (30A) Fuel pump relay, secondary air injection (AIR) pump relay, AC compressor clutch relay-316i/318i/330i
  5. F5: (30A) Ignitioncoilrelay-316i/318i/320i/323i/328i
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