Fuel and air

P01AB — Alternative Fuel Tank Temperature Sensor Performance

Severity: low Safe to drive

What P01AB means

The engine control unit compares the signal from the temperature sensor in the second (alternative) fuel tank with expected values and other temperature inputs. That temperature is used to estimate fuel density and meter fuel accurately. P01AB sets when the reading is unrealistic, stuck, or changes too slowly, even though the circuit is not clearly open or shorted.

Symptoms

  • Check Engine light on
  • Reduced fuel economy
  • Rough or unstable idle
  • Hard starting or forced switch to gasoline
  • Weaker performance on the alternative fuel

Possible causes

  1. Faulty alternative fuel tank temperature sensor
  2. Corroded, damaged or loose sensor connector
  3. Open, chafed or high-resistance wiring in the signal or ground circuit
  4. Moisture or contamination in the sensor or connector
  5. Rarely, an ECU software fault or calibration error

How to diagnose

  1. Scan all codes and freeze-frame data and look for related fuel system codes
  2. Compare the alt-tank fuel temperature in live data with ambient temperature on a cold engine
  3. Inspect the sensor connector and harness for corrosion, moisture and damage
  4. Measure sensor resistance and compare it with the manufacturer's temperature table
  5. Check reference voltage, signal wire and ground at the sensor and ECU
  6. Test the harness for opens and shorts
  7. If wiring and sensor are good, check for ECU software updates

Common fixes

  • Replace the fuel temperature sensor
  • Repair or replace damaged wiring and connectors
  • Clean the terminals and fix the source of moisture
  • Update or reflash the ECU if the manufacturer provides it

Questions and answers

What does P01AB mean?

The ECU found that the alternative fuel tank temperature sensor reading is implausible or does not match expectations. The cause may be the sensor, the wiring or, less often, the ECU.

Can I drive with code P01AB?

Usually yes, but fuel economy and running on the alternative fuel may suffer. Don't put off diagnosis for long.

How do I clear P01AB?

Clearing it with a scan tool only helps temporarily. If the fault remains the code will return, so check the sensor and wiring first.

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.