P2A79 code meaning
Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Intermittent/Erratic
Powertrain system Generic code P2Axx codes Check engine light
What P2A79 means
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.
P2A79 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2A79
- Uneven fuel pressure or surging power on gas
- Sporadic warning lamp that clears again
- Occasional false empty-tank message
Common causes of P2A79
- Most likelyLoose or fractured crimp terminal in the sensor circuit
- PossibleMoisture or ice in the sensor plug
- PossibleHarness damaged by vibration at the hydraulic unit
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 P2A79 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. |
| 79 | The exact fault in that area. |
What to do next
- Note P2A79 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 P2A79
What does P2A79 mean?
P2A79 means "Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Intermittent/Erratic". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P2A79?
Drive gently and only to a workshop. With P2A79 the car can go into limp mode (reduced power) to protect itself.
Will P2A79 fail an emissions test?
Yes, it can. P2A79 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 P2A79 to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will P2A79 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.