P2A79Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Intermittent/Erratic
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P2A79 records a hydraulic pump pressure signal that jumps or drops out for short moments without staying low or high long enough for P2A77 or P2A78. In a reciprocating LNG pump the controller reads this sensor continuously to find each stroke end, so a single spike can be mistaken for the end of travel and a brief dropout for a missing pressure peak. The pump may then run uneven strokes, and Westport's empty-tank logic, which counts low peaks over several strokes, can be misled. Vibration at the frame-mounted hydraulic unit, moisture in the plug and fractured crimps are typical causes. No manufacturer documents P2A79. Log the signal while flexing the harness; dropouts in an otherwise steady trace point to wiring.
- What you may notice
- Uneven fuel pressure or surging power on gas
- Sporadic warning lamp that clears again
- Occasional false empty-tank message
- Likely causes
- LikelyLoose or fractured crimp terminal in the sensor circuit
- PossibleMoisture or ice in the sensor plug
- PossibleHarness damaged by vibration at the hydraulic unit
- 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: €80 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.