P2A77 code meaning
Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Low
Powertrain system Generic code P2Axx codes Check engine light
What P2A77 means
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.
P2A77 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2A77
- Warning lamp with false empty-tank indication
- Unexpected switching between LNG tanks
- Gas supply stopped or reduced engine power
Common causes of P2A77
- Most likelySignal wire chafed through and shorted to ground
- Possible5 V reference open or pulled to ground
- Less likelyPressure sensor failed internally
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Alt fuel hyd pump pressure sensorWiring harnessAfcm
What each part of P2A77 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| A | Area: hybrid propulsion. |
| 77 | The exact fault in that area. |
What to do next
- Note P2A77 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P2A77
What does P2A77 mean?
P2A77 means "Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Low". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P2A77?
Drive gently and only to a workshop. With P2A77 the car can go into limp mode (reduced power) to protect itself.
Will P2A77 fail an emissions test?
Yes, it can. P2A77 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P2A77 to fix?
Difficulty: hard. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will P2A77 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.