Fuel and air

P01AA — Alternative Fuel Tank Temperature Sensor Circuit Fault

Severity: low Safe to drive

What P01AA means

The control unit monitors a temperature sensor in the alternative fuel tank or cylinder, such as a gas tank. Temperature is used to estimate fuel density and quantity and to manage delivery correctly. P01AA is stored when the signal is out of range or missing. The exact wording and set conditions vary by manufacturer.

Symptoms

  • Check Engine light on
  • Inaccurate alternative fuel level or range reading
  • Possible higher fuel consumption
  • Rough running or hard starting on alternative fuel (not always)
  • Code stored with no obvious symptoms

Possible causes

  1. Failed alternative fuel tank temperature sensor
  2. Open, shorted or chafed wiring
  3. Corroded or loose sensor connector pins
  4. Moisture or corrosion in the connector
  5. Faulty control unit or gas system module (rare)

How to diagnose

  1. Scan all codes and freeze frame data and look for other fuel system codes
  2. Inspect the sensor, connector and harness for damage, moisture and corrosion
  3. Check the sensor's temperature reading on a scan tool and compare it with actual temperature, watching for stuck or implausible values
  4. Measure sensor resistance and compare it with specifications
  5. Check for reference voltage and ground at the sensor connector
  6. Test the wiring from the sensor to the control unit for opens and shorts
  7. Clean the contacts, clear the code and see if it returns

Common fixes

  • Replace the alternative fuel tank temperature sensor
  • Repair or replace damaged wiring
  • Clean or replace the connector
  • Update software or replace the control module (rarely)

Questions and answers

What does P01AA mean?

It is a circuit fault in the alternative fuel tank temperature sensor. The control unit is getting an invalid signal from the sensor or none at all.

Can I drive with P01AA?

Usually yes, particularly on gasoline. Fuel quantity estimates and alternative fuel delivery may be less accurate, so have it diagnosed soon.

How do I fix P01AA?

Check the connector and wiring first, then the sensor itself. Repairing the harness or replacing the sensor usually fixes it, then clear the code.

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.