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I was driving on the freeway a couple weeks ago when I felt my car stall out, a 2002 c240. I got it towed home and the next day found the fuel pump fuse had popped. I replaced it with the same size fuse, a 20a fuse and it immediately popped. I tried a 25a just to see if it would last a little longer and allow the fuel pump to engage and again it popped..
I checked the power wire and the other wires in the harness and nothing was grounding out. I did a google search and a small Q&A forum and someone else had the same problem. The guy replaced the fuel pump relay and it was fine. I know relays hardly go bad but they do on occasion so I ordered a relay. Unfortunately, if you saw my other thread, I lost my only key to the car so I'm not able to test the new relay.
If that's not it, I know this is a common problem, its it pretty likely that the fuel pump is bad? Maybe it's stuck and the resistance is blowing the fuse? I believe there's 2 fuel tanks and a balancer/sender connects them, how likely is it that this part has gone bad?
Has anyone else had this problem and if so, what was the fix?
Check the plug at the fuel pump.
There may be corrosion on the brown wire or it may be burnt.
This is the ground wire. The corrosion will increase the resistance and pop the fuse.
Check to see that there isn't evidence of corrosion or burning especially where the ground wire meets the spade connector inside the plug.
Bought my car and it didnt run at the time because fuel pump wasnt running and when it did it blew fuses. This is a common issue that is vastly overlooked.
I checked it out and all spade terminals going in to the pump are clean. The ground when unplugged tests 0.2 ohms so it's a good ground and it stays at 0.2 when the harness is plugged in.
It's brilliant! Why did I not even consider this? Why waste m time checking out any other possibility that caused this to happen and pay the dealership to do the exact same things that I'm doing to determine that it is, in fact, the fuel pump. Besides, pulling the fuel pump is way easier than, say, replacing a $6 relay or inspecting the ground going into the unit.
I feel much better doing a process of elimination before buying a $150-250 brand new pump and installing it. If whatever it was that popped the fuse happened to, it's unlikely I know, but if it happened to fry the existing fuel pump, couldn't the same thing happen to the new one?
AHhh, I'm just being a smart *** man, I wish sarcasm could somehow translate threw a keyboard, I do thank you for posting, I didn't think a blown fuel pump fuse would be so uncommon 'round here.
Once I get my replacement key, maybe you saw my other thread, I lost my keys in an accident, I'll replace the fuse unplug the harness going into the fuel pump, and see if it pops, it it doesn't but once I plug it in, the fuse blows, it's be pretty clear that the fuel pump was indeed bad. If I unplug the harness and turn the key and it does blow instantly, like it has been, I'll meter each wire to ground then follow the harness to where ever it goes, find the break in the wire and replace it.
-Check the hot lead for continuity to chassis of car. If ~zero ohms, trace the wire from the connector back to the fuse; the short will be in there somewhere.
-While connector is off of pump, check the impedance of the pump. FWIW, fuses are usually rated 1.5 to 2 times the expected current. My car’s fuel pump draws ~13.6 amps at ~13.1 volts; that works out to an impedance of roughly one ohm. So…check from the pump’s connector to chassis for short circuit. It is possible your fuel filter is clogged, or the fuel pump is bad, and increased current is required to maintain fuel pressure. Also check the socket into which the fuel pump relay plugs; the relay and socket on my car literally melted (root cause was a clogged fuel filter. I won't delay on that maintenance ever again.).
-FWIW, on my car, the overcurrent condition embrittled the insulation on the wires at the connector. The wires were also pressed against the metal cover that shields the fuel pump. No short occurred but I caught it and repaired it prior to problems occurring.
Hi bigian. You did the right thing by doing all the tests first. I said replace the fuel pump only because I have experience in what blows that fuse. And don't worry there is no way you can damage a new pump if there was indeed a wiring issue. Also the only thing that will cause a fuse to blow is over current. Meaning the positive goes to ground before the pump or internally in the pump. Never an open circuit. You will find it very rare that the wiring shorts to ground in that loom. Good luck
I may be suffering from dehydration after working on the car all day, but I can't quite figure out where to plug all the wires from the new harness.
Why are these split? Do they go into the neighboring relay? I don't think I saw any fuses nearby, but I'll check again, and I have an early 2003.
Also colors seem to have changed, my relay has:
- brown/green for the thin wire which goes to the ME.
- thick red/yellow
- thick red/blue
- thin red/white
I have most of the car apart, and the front wire tunnel exposed, so its simple right now as long as I figure out where everything connects.
I recently picked up a clean 05S500 with less than 40k miles and as I've been driving it I've noticed when I fill up the range only hits 142 miles. I’ve also noticed after driving a little the fuel will go down and if I turn it off and turn it back on it goes back too 23 gallons. What could be the problem?
09-05-2015, 04:10 AM
I do thank you for posting, I didn't think a blown fuel pump fuse would be so uncommon 'round here. 
