P Fay

Three days working on this with no luck. All was fine with the car until my wife tried starting one morning.
Cranks, but no start, no fuel pressure. Replaced CPS, fuel pump relay, and checked every fuse.
There are 0 volts at fuel pump, and 0 at pump fuse when cranking. No pump sound when cranking.
What could be keeping the circuit to the pump open? Is there some input to the relay that would disable the pump circuit?
2004 Mercedes Benz C 240 4MATIC Wagon (203.281), V6-2.6L (112.916)

Thanks

P Fay

Any suggestions out there?

P Fay

I'm now suspecting the sending unit may not be sending a signal, and ECU thus not powering the pump.... We'll see.

Russell Ormerod

Bridge the relay! Does pump run?

Russell Ormerod

Sender has nothing to do with pump function

P Fay

Thanks for the tip. I bridged the relay (leads 3 & 5) - no pump sound when turning key, no start, no fuel.
So I should assume I need a new pump? I want to be sure before dropping $260 for a pump (I assume unreturnable).

Russell Ormerod

If you bridge the relay you should have power at the pump. With power and still no pump running then yes you need a new one. Look carefully at the terminals at the pump and the plug sometimes they get hot and melt

P Fay

Finally, I can confirm there is power to the pump (Blk/Grn lead). But the pump is dead. I'll order a new one and hope that solves the problem.


Fuel pump wiring

Russell Ormerod

Good

P Fay

I was going around in circles - testing the wrong color wire. Finally got that straightened out.
Then I tried to order the wrong assembly part on the left side, the same side as the power supply, but the pump is on right. Luckily the parts guy caught that error for me since the diagrams call both sides the "pump".
I'd go broke if I had to do this for income.

Thanks kindly for the advice and hints.

slammer111

The pump tends to die at the 200-250k km mark. Guessing you're due based on the year of your car.

You might want to add your location in your signature. Helps the rest of us know what version of the car you have.

See link below. The fuel pump is in the hatch on the R side of the car. I'm not sure the unit on the L side is known for failing. Still running on the original unit on this end.

W203 fuel pump replacement

One thing I learned from the experience is that the pump is cooled by gasoline in the tank. They aren't kidding when they say not to drive the car below 1/4 tank. I used to run my tank to almost empty every time. Probably not the best idea.

While you're at it, make sure your fuel filter has been changed at some point. The service life is 120k km, though it can probably last longer. Only get the OEM MB (dealer) or Mahle (OE) units. Other (cheaper) aftermarket brands are known to have faulty pressure regulating valves inside which cause problems down the road.

W203 fuel filter replacement

P Fay

Thanks, I'm getting a filter also. I never buy aftermarket.