What does it mean?
The opposite of a low pressure fault, this code means the gaseous fuel rail is holding more pressure than the strategy allows. The regulator or vaporiser is supposed to knock high tank pressure down to a stable working pressure at the rail, and the module monitors that value against a maximum limit with a short filter time. When the measured pressure exceeds that limit, the module stores the code, because excessive rail pressure makes every injector pulse deliver more gas than calculated and drives the mixture rich. It also stresses the rail, hoses and injector seals, so most systems will shut gas operation down and revert to gasoline as a safety measure. The usual root cause is a regulator that cannot close or vent properly, rather than anything in the sensor circuit.
Symptoms
- Rich running on gas, black smoke and a strong exhaust smell
- MIL (check engine lamp) on, often with rich mixture codes alongside the gas system fault
- Rough idle, poor throttle response and hesitation on gas
- Automatic shutdown of gas operation and a return to gasoline
- High gas consumption and negative gas fuel trims
- Gas smell around the regulator if a relief valve has lifted
Likely causes
- Pressure regulator stuck open or with a failed diaphragm, so rail pressure follows tank pressure
- Contamination or LPG heavy end deposits jamming the regulator seat
- Failed or disconnected regulator control solenoid, leaving the regulator at maximum output
- Blocked return or vent path where the system uses one, so pressure cannot bleed off
- Rail pressure sensor drifted high and reporting pressure that is not really there
- Vaporiser overheating because of an incorrect coolant circuit, raising gas pressure
- Wrong or non-approved regulator fitted during a previous conversion or repair
How to fix it
- Compare the scan tool rail pressure with a mechanical gauge on the rail; if the gauge is normal, the sensor has drifted and the regulator is innocent
- Check the regulator control solenoid for supply, ground and command from the module, and confirm it responds when actuated with a scan tool
- Inspect the regulator for external damage, oily residue and a leaking diaphragm, and check that the vent path is clear
- Verify the coolant supply and return at the vaporiser are correctly connected and that the unit is not running abnormally hot
- Watch rail pressure at key on, at idle and under load; a rail that tracks tank pressure proves the regulator is not controlling at all
- Service or replace the regulator with the correct approved unit, then recheck the pressure across the full load range
- Replace the rail pressure sensor only when the mechanical gauge proves the real pressure is correct