In a hydraulically driven LNG pump system the controller watches the oil pressure delivered by the hydraulic pump. Westport's patent US8726785B2 places this sensor in the supply line between the hydraulic pump outlet and the hydraulic drive, using it for three jobs: reversing the drive at each stroke end, spotting an empty tank when peak pressure stays low, and flagging leaks or other abnormal conditions. Caterpillar's design likewise feeds supply and return pressure to the controller to shift its directional valve. P2A75 is the general circuit fault of this hydraulic pump pressure sensor. Without the signal, the pump cannot be cycled correctly and LNG delivery may stop. No manufacturer publishes P2A75; P2A77 and P2A78 cover low and high.
High severity. Can I keep driving?If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.
Symptoms
- Check engine light on
- LNG pump stops or strokes irregularly, gas pressure drops
- Dual-fuel engine runs on diesel only or with reduced power
Most likely causes
- Connector or harness at the hydraulic pressure sensor damaged
- Hydraulic pump pressure sensor faulty
- Sensor supply or ground disturbed
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P2A75 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- A: Hybrid or air and fuel
- 75: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2A75?
If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.
What causes code P2A75?
The most common causes are: connector or harness at the hydraulic pressure sensor damaged; hydraulic pump pressure sensor faulty; sensor supply or ground disturbed.
Related codes
- P2A76Alternative Fuel Hydraulic Pump Pressure Sensor Range/Performance
- P2A77Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Low
- P2A78Alternative Fuel Hydraulic Pump Pressure Sensor Circuit High
- P2A79Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Intermittent/Erratic
- P2A7AAlternative Fuel Hydraulic Pressure Sensor Circuit
- P2A70Alternative Fuel Hydraulic Fuel Pump Select Valve Control Circuit
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.