Fuel and air

P01B3 — Alternative Fuel Tank 'A' Level Sensor Circuit Intermittent/Erratic

Severity: low Safe to drive

What P01B3 means

The engine control module monitors the voltage in the level sensor circuit of the alternative fuel tank 'A', such as a CNG/LPG tank or a second fuel tank. The signal normally changes smoothly as fuel is used. P01B3 is stored when the signal drops out, jumps around or doesn't make sense, which points to an intermittent fault.

Symptoms

  • Fuel gauge for the alternative tank jumps or fluctuates
  • Fuel level shown inaccurately on the dash
  • Check Engine light on with no other drivability problems
  • Level reading drops out and returns at random

Possible causes

  1. Damaged sensor wiring (open, chafed or intermittently shorted)
  2. Poor contact or corrosion in the sensor connector
  3. Failed level sensor in the alternative tank
  4. Unstable power supply or poor ground to the sensor
  5. Rarely, a faulty ECM

How to diagnose

  1. Scan for codes and freeze frame data, and note any other fuel system codes
  2. Watch the tank level signal in live data for jumps or dropouts
  3. Inspect the sensor connector for corrosion, moisture and loose or bent pins
  4. Wiggle the harness and connector while watching the scan tool to see if the signal glitches
  5. Check the wiring for opens, chafing and shorts to ground or voltage
  6. Measure the sensor reference voltage and ground circuit resistance
  7. Test sensor resistance at different fuel levels against specifications
  8. If wiring and supply are good, replace the sensor, then suspect the ECM

Common fixes

  • Repair the wiring harness or replace a damaged connector
  • Clean the terminals and restore a solid connection
  • Replace the alternative fuel tank level sensor
  • Correct the sensor power or ground fault
  • Clear the code and confirm it doesn't return

Questions and answers

Can I drive with P01B3?

Usually yes, since it rarely affects how the engine runs. But the level reading may be wrong, so refuel early to avoid running out.

What most often causes P01B3?

Most often it's a poor connection in the sensor connector or a damaged wire. If the wiring is fine, the sensor itself is the next suspect.

Will P01B3 go away on its own?

The light may turn off if the fault doesn't recur over several drive cycles, but the cause is still there. It's better to find the bad contact or failing 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.