P2A77Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P2A77 is set when the signal from the hydraulic pump pressure sensor drops below the range a working sensor can deliver, typically because the signal wire or the 5 V reference is shorted to ground or the reference feed is open. On hydraulically driven LNG pumps this matters more than a mere missing value: Westport's patent US8726785B2 treats a peak hydraulic pressure that repeatedly stays low as the sign of an empty vessel, so a reading stuck near zero can mimic an exhausted tank and trigger needless tank switching or a fuel shutdown. No manufacturer publishes P2A77 or its voltage limits. Check the sensor connector, the reference voltage at the plug and the harness along the frame. P2A78 is the high counterpart.
- What you may notice
- Warning lamp with false empty-tank indication
- Unexpected switching between LNG tanks
- Gas supply stopped or reduced engine power
- Likely causes
- LikelySignal wire chafed through and shorted to ground
- Possible5 V reference open or pulled to ground
- RarePressure sensor failed internally
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.