Fuel and air

P01AC — Alternative Fuel Tank Temperature Sensor Circuit Low

Severity: low Safe to drive

What P01AC means

The engine control unit monitors the signal voltage from the temperature sensor in the alternative fuel tank, such as a CNG or LPG tank. The sensor is a thermistor, and the ECU uses its reading to correct fuel delivery for gas density. P01AC sets when the signal voltage falls below the expected range, most often from a signal wire shorted to ground or a failed sensor.

Symptoms

  • Check Engine Light on
  • Increased fuel consumption
  • Possible reduced power or rough running on alternative fuel
  • Automatic switch to gasoline on some vehicles
  • Inaccurate gas range or level readings

Possible causes

  1. Failed alternative fuel tank temperature sensor
  2. Signal wire shorted to ground from damaged insulation
  3. Damaged wiring harness or corroded connector pins
  4. Moisture in the sensor connector
  5. Faulty ECU or gas control module (rare)

How to diagnose

  1. Scan for codes and review freeze frame data; note any other alternative fuel codes
  2. Inspect the sensor connector and harness for damage, chafing, moisture and corrosion
  3. Compare the scan tool temperature reading with the actual tank temperature; a stuck or extreme value points to a fault
  4. Measure the sensor resistance and compare it with the specification for that model
  5. Unplug the sensor: if the code changes to circuit open, the fault is in the sensor or wiring up to the connector
  6. Check the signal wire for a short to ground and confirm reference voltage (typically about 5 V)
  7. Test wire continuity to the ECU or gas control module and check the ground
  8. Clear the code and confirm it does not return after the repair

Common fixes

  • Replace the tank temperature sensor
  • Repair or replace the damaged wiring harness
  • Clean or replace the corroded connector and seal it against moisture
  • Replace or reflash the control module only after ruling out everything else

Questions and answers

Can I drive with P01AC?

Usually yes, since it is not a safety-critical fault. Fuel use may rise and operation on alternative fuel may become unstable, so get it diagnosed soon.

What most often causes P01AC?

Most often a failed temperature sensor or damaged wiring or a connector shorted to ground. Start by inspecting the connector and harness.

Will the code clear itself?

If a poor connection caused it, the light may go out after several drive cycles. The code will return until the underlying fault is fixed.

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.