Fuel and air

P01A1 — Alternative Fuel Tank A Pressure Sensor Circuit High

Severity: medium Safe to drive

What P01A1 means

The engine control module (ECM) detected a voltage from the alternative fuel tank A pressure sensor that is above the expected range. This sensor normally outputs a signal proportional to tank pressure, typically on a CNG, LPG or other non-gasoline fuel system. A high reading usually points to a bad sensor, a short to voltage or an open in the signal circuit, and only rarely to truly excessive pressure.

Symptoms

  • Check Engine light on
  • Higher fuel consumption
  • Unable to run on the alternative fuel, or automatic switch to gasoline
  • Possible hesitation or rough running
  • Implausible tank pressure reading on a scan tool

Possible causes

  1. Damaged, corroded or loose wiring harness or connector at the sensor
  2. Signal wire shorted to voltage
  3. Failed tank pressure sensor
  4. Poor ground or unstable 5 V reference supply
  5. Actual excessive tank pressure or a faulty valve
  6. Rarely, a faulty ECM

How to diagnose

  1. Read all codes and freeze frame data, clear the code and see if it returns
  2. Inspect the sensor, connector and harness for damage, moisture, corrosion and chafing
  3. Check for fuel gas odor and leaks in the alternative fuel system
  4. Compare the scan tool pressure reading with a gauge reading with the engine off
  5. Use a multimeter to check the 5 V reference and ground at the sensor connector
  6. Test the signal wire for a short to voltage or an open circuit
  7. Swap in a known good sensor or test it per the factory wiring diagram

Common fixes

  • Repair or replace the damaged wiring and connector
  • Replace the alternative fuel tank A pressure sensor
  • Restore the sensor's power or ground supply
  • Correct the cause of real overpressure in the tank or fuel lines
  • Update software or replace the ECM if it is confirmed faulty

Questions and answers

What does P01A1 mean?

The ECM sees too high a signal from the alternative fuel tank A pressure sensor. Most often it is the sensor or its wiring rather than real pressure.

Can I drive with P01A1?

Usually yes, often on gasoline. But if you smell fuel gas or the tank pressure is truly high, stop and have the system inspected.

How do I fix P01A1?

Start by inspecting the sensor wiring and connector and checking its power and ground. If the circuit is good, replace the pressure sensor.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.