Fuel and air

P01AF — Alternative Fuel Tank A Level Sensor Circuit Fault

Severity: low Safe to drive

What P01AF means

The engine control unit monitors the signal from the level sensor in alternative fuel tank A, such as a CNG or LPG tank, to estimate how much fuel is left. If that signal goes out of range or disappears, for example from an open or short circuit, the unit sets P01AF and turns on the check engine light.

Symptoms

  • Check engine light on
  • Alternative fuel gauge reads incorrectly
  • Gauge jumps or sticks on empty or full
  • Unexpected switch to gasoline
  • Hard to judge remaining range on gas

Possible causes

  1. Faulty level sensor in the alternative fuel tank
  2. Damaged wiring or corroded sensor connector
  3. Open circuit or short to ground or power in the signal wire
  4. Poor sensor ground connection
  5. Rarely, a fault in the control module

How to diagnose

  1. Scan all codes and freeze frame data, clear P01AF and see if it returns
  2. Compare the scan tool fuel level reading with the actual amount in the tank
  3. Inspect the sensor connector and harness for damage, moisture and corrosion
  4. Check supply voltage, reference voltage and ground at the sensor connector
  5. Test the sensor signal and resistance as the level changes, per specifications
  6. Test the signal wire for opens and shorts back to the control module
  7. If the wiring is good, replace the sensor and retest

Common fixes

  • Replace the alternative fuel tank level sensor
  • Repair or replace damaged wiring and connectors
  • Clean terminals and restore the ground connection
  • Clear codes and road test to confirm the repair
  • If the fault persists, test and if needed replace the control module

Questions and answers

What does P01AF mean?

It is a circuit fault in the alternative fuel tank A level sensor. The control unit is getting a wrong or unstable signal about how much fuel is in the tank.

Can I drive with code P01AF?

Usually yes, but don't trust the alternative fuel gauge. Keep enough gasoline in the tank in case the gas runs out sooner than expected.

How do I fix P01AF?

Start by inspecting the sensor wiring and connector and testing the circuit. If those are fine, the level sensor itself usually needs replacement.

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.