I changed my fuel pump, now I have no power to the pump. Fuse and relay, no power. Could the problem be the control module ? Can it be tested? no code showing up.
2011 E550

 

lets see if I can find the wiring diagrams for that....

is that car a 212.072 with the M273.971, or 212.073 with the M278.922, or what? actually, if you can post your VIN, it makes it much easier to find wiring diagrams in WIS.... I'm gonna take a stab that its the M273 in 2011...


looks like the fuel pump M3 is directly powered by the Fuel Pump Control Unit (FPCU) N118.

N118 gets its power from fuse F42 in the rear SAM/fusebox, via N118 pin 1, and ground from the right footwell ground point W15/1 vio N118 pin 2

If this is like most every car I've worked on, the fuel pump only runs for a second when you turn the ignition on, then starts back up when the crank position sensor indicates the engine is turning over. I don't see a direct connection to the CPS, so odds are that comes in via digital messaging on CAN C

 

Thanks, It is the M273 code. I assumed the pump should come on till the line is fully pressured. I have no fuel manifold pressure.

 

soooo. I would locate N118, the FPCU, and backprobe connector 1... connector 1 pin 1 (red/white) shoudl be +12V, pin 2 (brown) should be ground. pin 3 should be power to the fuel pump (red/blue), pin 4 (brown/red) should be ground from the fuel pump.

here's the 'basic function' document. seems to indicate this FPCU is under the right rear seat closest to the door.


edit, oh they refer to it as the FSCU, Fuel System Control Unit.

 

also, the FSCU is on CAN C, so it should have diagnostics via XEntry or another Mercedes specific diag app/tool.

per that last PDF, if you replace it, the replacement has to be coded by XEntry to match the car.

 

Thanks, Having trouble getting the trim off to get at the FCU. Does the back of the seal need to come out for access?

 

I don't know, I've never messed with mine.

I don't see any R&R instructions on the FSCU in WIS.

 

Did you bench test the fuel pump?

 

You explanation is confusing.

Fuse and relay, no power.
There is no relay for N118 fuel control module, there is only Fuse 42 for N118, based on assumed N118 diagram for your car.
Note I say assumed because between facelift and before facelift model there could be differences on fuse assignment for N118. I am not in front of my PC till mid Jan 2023 and I can't access WIS.
So what do you mean by Fuse and relay, no power. ? Which fuse did you inspect and which relay you thought belongs to fuel system ?

Take photo of the cables into the fuel pump. Its color and total cable numbers. There are 2 version, simple 12V DC fuel pump and the 3 phase one. Mine is a 3 phase one.
The fuel pump is at the RIGHT side of the rear seat and its wire harness is connected to N118. You can fish out the N118 without needing to remove the plastic trim .
N188 locks down using plastic notches only, no screws whatsoever. I am basing on my N118 which I have once removed.
Use this as N118 casing shape reference : https://www.ebay.com/itm/36385508819...3ABFBMmPOe16dh

If you want to test N118, without Xentry or capable bi-directional scanner, you can't.
You can command ON for fuel pump using Xentry or suitable scanner.

However, check all basic power(+) and ground(-) first into and out of N118. If your pump is a simple 2 wire 12V version and not a 3 phase one, it is easier to troubleshoot.
However without a proper scanner and you can't confirm proper CAN BUS operation aka no error code of CAN BUS to N118, you can't troubleshoot the command side and only
knowing power is available, your troubleshooting will not be effective.

ADD:
For my N118 and fuel pump, it will not run unless engine is cranked to start. Maybe different to yours.
Some cars will pre-primed the fuel system with ignition key ready to crank position 2.
Some BMW will pre-primed the fuel system with a mere door opening.

 

a 2011 E550 is engine M273 and most certainly pre-facelift. the wiring diagram shows its a 2-wire 12V pump, but the Basic Functions page I attached says its pulsed and not just switched on.

 

If pulsed it is probably PWM and would seems so if fuel system is returnless and no other means of pressure regulation device.
I don't know if 3 phase fuel pump is only for facelift model or some bigger engine V8 before facelift also get 3 phase fuel pump ?

Good for OP if 2 wire version fuel pump, easy to test without N118.

 

I dunno, but the world of fuel returns and simple mechanical bypass fuel pressure regulators sure seems a lot simpler.

 

indeed, engine M276, M278 use the three wire pump, and those three wires are labeled as phase V, phase W, phase U.... since there's no ground, its a 'delta' 3-phase, so its not something you can just power to spin up, you need to coordinate those 3 phases in time, something like this but probably with square waves rather than the pretty sinewaves shown here...

 

See attachments.