S211 E55 AMG 2003 ........Where is my fuel pump relay?

[DreamCatcher88]

Could someone assist, please?

Where is my E55 Fuel Pump Relay for the 2003 S211 E55 AMG Estate?


The dual fuel pumps have failed; the vehicle cranks but does not start.
My multimeter indicates that there is no power to the pumps when the ignition is activated and the engine is turning.

The vehicle commenced operation immediately and functions when direct current is supplied to the wiring of one pump located beneath the offside rear seat - RED/YELLOW wire and BROWN wire!
I have located what appears to be the fuse labelled '90' - refer to the attached image. The top is broken off, yet it remains fully intact and operational, exhibiting no indications of damage or overheating. However, the location of the relay is unclear.
I assume that both the relay and the connector may be damaged.

The fuse and relay diagram provided with the vehicle, located behind the driver's dashboard side panel, indicates that fuse F04 (20A) in the rear N/S SAM and fuse bank—behind the left-hand boot side panel—is associated with Relay 'A', the first from the bottom. However, I have discovered that this information is inaccurate; fuse F04 and the small Relay 'A' are designated for the intercooler pump in E55 AMG models.
Some owners in the US indicate that the fuse and relay are located behind the right-hand side panel of the trunk; however, this appears to apply solely to sedan vehicles, not station waggons.

The internet and AI are fraught with inaccuracies.

I appreciate your assistance in advance.

[DreamCatcher88]

Upon tracing the wiring from the pumps, I ultimately discovered the solitary fuel pump relay that was incinerated.
Connected a spare 40A relay for testing, and the vehicle started immediately with optimal fuel pressure.


The positive pump wires are RED/BLUE, not RED/YELLOW as previously indicated - please refer to the attached picture.
The RED/YELLOW positive wires originate from the 90A Green Fuse located at position 90 in the rear pre-fuse box beneath the trim on the right side of the spare wheel well.

It was concealed deep within the right-hand baggage compartment of the HK Subwoofer.
Remove the 5x10mm screws, pivot the subwoofer aside, and you will observe its attachment to the wheel arch.
Certain later E55 versions are equipped with dual relays.

Now upgraded to a high-quality single 60A, as it was operating at elevated temperatures when replaced with a 40A. Operates at a significantly lower temperature!

[DreamCatcher88]

[Rudy7831]

The pumps contain a fine mesh filter within the housing, which becomes obstructed with time, causing the pump to exert excessive effort and ultimately fail. It appears that the relay might have prevented this issue; however, I recommend removing the pump housings at your earliest convenience to replace the mesh filter.

On my previous E55, the vehicle would achieve optimal performance during regular driving; but, on a dynamometer under stress, the fuel pumps exhibited weakness and the air-fuel ratio fluctuated significantly. Upon the replacement of the pumps, the car was transformed; it felt like an entirely different engine. I possess a thread located here at some point.

[DreamCatcher88]

Thank you for the information. I will clean the pumps and mesh, change the filter on the opposite side, and test the fuel pressure under full load.
The fuel pressure at the rail appears satisfactory at '83 PSI', decreasing to '76 PSI' after thirty minutes with the pumps deactivated. I intend to replace the pumps for reassurance.

[DreamCatcher88]

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