P01A1
Alternative Fuel Tank A Pressure Sensor Circuit High.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 1
- AreaFuel and air metering
- A1
- FaultThe specific fault in that area
What it means
P01A1 means the control unit saw the signal from the alternative fuel tank A pressure sensor sitting higher than its expected range. This points to a 'circuit high' fault such as a short to voltage, a damaged reference or signal wire, or a faulty sensor. It only applies to vehicles fitted with an alternative fuel system, such as CNG or LPG, and the exact sensor location and layout depend on the model and installation.
Symptoms
- Engine warning light on
- Alternative fuel mode unavailable, or the car stays on petrol on a bi-fuel model
- Fuel gauge or gas level reading missing or wrong for the alternative fuel
- Poor running or reduced power while on alternative fuel
- Difficulty starting on alternative fuel or an unexpected fuel switchover
Possible causes
- Faulty tank A pressure sensor reading high internallylikely
- Signal wire shorted to a voltage supply or to the 5 volt referencelikely
- Damaged, corroded or water-affected connector or terminals at the sensor or control unitlikely
- Open circuit in the sensor ground, which can push the signal highpossible
- Fault in the alternative fuel control unit or the engine control unit sensor supplyrare
- Actual tank pressure beyond the sensor's range because of a system faultrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, and note whether other sensor supply or alternative fuel codes are present.
- Check for any smell of gas and listen for leaks around the tank, lines and valves before working on the system. Follow the manufacturer's safety procedure for the fuel type.
- Visually inspect the sensor, wiring and connectors for chafing, heat damage, corrosion, moisture and bent or pushed-back pins.
- View live data for tank A pressure with the ignition on and compare it with the expected value for the known tank condition. Check whether it is stuck at the top of its range.
- With the ignition on, measure the sensor reference voltage, ground and signal at the connector against the model's wiring data.
- Unplug the sensor and watch the live reading. If it stays high, look for a signal wire short to voltage or a control unit fault. If it changes, suspect the sensor.
- Check the signal wire for continuity and for shorts to voltage or to the reference wire, with the control unit connector disconnected.
- Check the manufacturer's data for any known software updates or model-specific tests for the alternative fuel system.
How to fix
- Replace the tank A pressure sensor if it is faulty, following the correct depressurising and sealing procedure for the fuel system.
- Repair or replace damaged wiring that is shorted to voltage or open on the ground or signal circuit.
- Clean or replace corroded or damaged connectors and terminals, and make sure they are properly seated and sealed.
- Repair any underlying fault in the alternative fuel system that is causing a genuine overpressure.
- Have a control unit fault diagnosed and repaired, or update its calibration only if the manufacturer lists it as a known fix, once the wiring and sensor are proven good.
Can I keep driving?
If there is no smell of gas and the car runs normally, it can usually be driven, and on a bi-fuel car it may run on petrol, but get it checked soon. If you smell gas or suspect a leak, stop driving and have the system inspected by a qualified technician.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.