Code P0090, fuel relay?

Hello,

P0090 - fuel pressure regulator 1
The fuel pressure regulator is located at the back of the high-pressure diesel pump.
See image 2 below.

This fault usually sets if the rail pressure is lower than desired.
The rail pressure is sent by the rail pressure sensor to the ECM.
At cranking we should see rail pressure of more than 200 Bar, 2900psi.
This you can check using a suitable diagnostic tool, it will show actual and desired pressure.

Also check that fuel pressure regulator 2 is shut while cranking, this you can checked by removing the leak off pipe at the rail. Ensure no fuel leaks out while cranking.
See image 1 below.

Check that the in-tank fuel pump is activating and is supplying around 4-5 Bar, 58-72 psi of fuel pressure to the fuel filter. The in tank fuel pump should deliver around 1L of fuel per minute. The fuel is then transferred to the high-pressure pump at the engine. A bad/blocked fuel filter can also cause this issue.

Fuel pump pressure test:
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Suggest inspecting the fuel filter element for possible metal deposits

At times we can see the in tank fuel pump deposit metal filings into the fuel supply system, these usually settle in filter, high pressure pump control valve, rail pressure sensor, injectors etc.

Hope this helps.

Cheers, Boris

Hello,

Please let us know if we can assist with more information.

Good luck.

Cheers, Boris

It looks like there is a fuel pump control module that runs the fuel system which I have seen go out. Here is the wiring diagrams so you can see what I am talking about. Check out the images (below). Please let us know what happens.

Sounds good, upload images of anything we should see to help fix the problem.