P0091: Fuel System Fault

P0091 on the Mercedes Sprinter VS30 falls under the fuel system fault group for the OM642 V6 diesel. The ECU sets this code when it detects an out-of-range condition in this system. Use the symptoms, common causes, and diagnostic steps below as a starting point, and always read the live data and freeze-frame for this specific code before replacing parts. If you're searching for the P0091 Mercedes Sprinter fix or P0091 VS30 / OM642 information, start with a full scan to capture any related codes stored at the same time.

• Reduced engine power or hesitation
• Hard starting or extended cranking
• Possible limp mode
• Check engine light
• Rough idle

• Fuel injector wear or leakage
• Fuel rail pressure regulation fault
• Clogged fuel filter or restricted supply
• High-pressure pump wear
• Sensor or wiring fault in the fuel system

1. 1Scan and record all codes, noting any related fuel codes stored together.
2. 2Review freeze-frame data for rail pressure, fuel temperature, RPM, and load.
3. 3Inspect fuel lines, the filter, and connections for leaks or restriction.
4. 4Monitor live rail/supply pressure (actual vs. commanded) at idle and under load.
5. 5Test the suspect sensor, valve, or injector against Mercedes spec.
6. 6Repair or replace the failed component, then clear codes and verify the fix on a road test.

1. 1Replace a clogged fuel filter and confirm a clean, unrestricted supply.
2. 2Replace a worn or leaking injector (and re-code it if required).
3. 3Repair fuel leaks or restrictions in the supply and return lines.
4. 4Replace a faulty rail-pressure sensor or pressure-regulating valve.
5. 5Replace a worn high-pressure pump when delivery is out of spec.