Engine derates or will not start; fault code indicates low fuel rail pressure during cranking or load.

Safety: Diesel fuel is flammable and under high pressure. Do not loosen high-pressure lines with the engine running. Wear eye protection and gloves.

• Check fuel level and supply valves: Confirm the day tank or main tank has adequate fuel and that all manual shutoff valves to the engine are fully open.
• Replace fuel filters: Replace the primary (pre-filter/water separator) and secondary (engine-mounted) fuel filters with Volvo Penta-approved elements. Prime the system using the hand primer or electric lift pump until all air is purged.
• Inspect for air leaks: Look for wet fittings, cracked hoses, or loose clamps on the suction side between tank and lift pump. Tighten or replace as needed. Air leaks often show as bubbles in clear lines or filter bowls.
• Check water separator: Drain water from the primary filter bowl. If large amounts of water are present, drain and clean the tank and replace filters again.
• Test rail pressure sensor and relief valve: Using diagnostic software (Volvo Penta VODIA or equivalent), monitor rail pressure during crank and load. If commanded vs actual pressure differ significantly and filters are new, suspect a failing high-pressure pump, leaking injector, or faulty rail pressure relief valve. These components should be tested and replaced by a qualified technician.