Cause
Faulty alternative fuel pressure sensor
One of the pressure sensors in a gaseous fuel system has failed or drifted.
A gas system measures pressure in more places than a petrol one, because pressure is what keeps the fuel in the right phase. There is tank pressure, the pressure arriving at the regulator, the pressure in the rail, and on liquid-injection systems the hydraulic pressure that stops the fuel boiling before it reaches the injector.
Which sensor is named tells you where to look, and the differences between them are the diagnosis. A healthy tank pressure with a low regulator inlet pressure means a restriction between the two — the line, the shutoff valve, or most often a filter nobody has changed since the conversion was fitted. A pump making pressure into a system that is not holding it means a leak rather than a pump.
A drifted sensor mis-fuels the engine rather than mis-reporting a gauge. Reading high, the module under-delivers and the engine runs lean, which on gas means high combustion temperatures and, over time, damaged valve seats. That is the expensive failure mode of a cheap part, and it is why a lean-running conversion should be diagnosed rather than tuned around.
These sensors are frequently combined with a temperature sensor in one housing, so replacing the assembly often settles both.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (25)
Codes where this is a likely explanation first, rather than merely a possible one.
- P2A69 Alternative Fuel Rail Pressure Regulator Inlet Pressure Sensor Circuit Likely for this code High
- P2A6A Alternative Fuel Rail Pressure Regulator Inlet Pressure Sensor Range/Performance Likely for this code High
- P2A6B Alternative Fuel Rail Pressure Regulator Inlet Pressure Sensor Circuit Low Likely for this code High
- P2A6C Alternative Fuel Rail Pressure Regulator Inlet Pressure Sensor Circuit High Likely for this code High
- P2A6D Alternative Fuel Rail Pressure Regulator Inlet Pressure Sensor Circuit Intermittent/Erratic Likely for this code High
- P2A75 Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Likely for this code High
- P2A76 Alternative Fuel Hydraulic Pump Pressure Sensor Range/Performance Likely for this code High
- P2A77 Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Low Likely for this code High
- P2A78 Alternative Fuel Hydraulic Pump Pressure Sensor Circuit High Likely for this code High
- P2A79 Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Intermittent/Erratic Likely for this code High
- P2A7A Alternative Fuel Hydraulic Pressure Sensor Circuit Likely for this code High
- P2A7B Alternative Fuel Hydraulic Pressure Sensor Range/Performance Likely for this code High
- P2A7C Alternative Fuel Hydraulic Pressure Sensor Circuit Low Likely for this code High
- P2A7D Alternative Fuel Hydraulic Pressure Sensor Circuit High Likely for this code High
- P2A7E Alternative Fuel Hydraulic Pressure Sensor Circuit Intermittent/Erratic Likely for this code High
- P2A6E Alternative Fuel Rail Pressure Regulator Inlet Pressure Too Low High
- P2A6F Alternative Fuel Rail Pressure Regulator Inlet Pressure Too High High
- P2A8B Alternative Fuel Vaporizer A Performance High
- P2A8C Alternative Fuel Vaporizer B Performance High
- P2A8D Alternative Fuel Vaporizer C Performance High
- P2A8E Alternative Fuel Pump A Performance High
- P2A8F Alternative Fuel Pump B Performance High
- P2A90 Alternative Fuel Pump C Performance High
- P2A9D Alternative Fuel High Pressure System Small Leak High
- P2AA2 Alternative Fuel Return Line Insufficient Flow High
Information, not instruction
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