Fuel and air

P01B1 — Alternative Fuel Tank 'A' Level Sensor Circuit Low

Severity: low Safe to drive

What P01B1 means

The engine control unit monitors the signal voltage from the fuel level sensor in the auxiliary (alternative) tank 'A'. Normally the sensor changes its resistance as the float moves, keeping the signal within a set range. P01B1 sets when the signal drops below that range, which usually points to a short to ground, an open circuit or a failed sensor.

Symptoms

  • Check Engine light is on
  • Inaccurate or very low fuel level reading
  • Gauge for the auxiliary tank reads empty after filling
  • Fuel system warning messages on some vehicles

Possible causes

  1. Failed fuel level sensor in tank 'A'
  2. Damaged wiring or signal wire shorted to ground
  3. Corrosion or poor contact at the sensor connector
  4. Open or corroded power or reference voltage circuit to the sensor
  5. Rarely, a fault in the control module reading the sensor

How to diagnose

  1. Scan all codes and freeze frame data, note them, clear the code and see if it returns
  2. Compare the scan tool fuel level reading with the actual amount of fuel in the tank
  3. Inspect the harness and sensor connector for damage, chafing, moisture and corrosion
  4. Unplug the connector and check reference voltage and ground against the wiring diagram
  5. Measure sensor resistance at different float positions and compare to specification
  6. Test the signal wire for a short to ground and for an open circuit
  7. If the wiring is good, check the module that reads the sensor signal

Common fixes

  • Clean or replace corroded terminals and the connector
  • Repair or replace damaged wiring
  • Replace the tank 'A' fuel level sensor
  • Replace or reprogram the control module if it is confirmed faulty

Questions and answers

Can I drive with code P01B1?

Usually yes, as the engine itself normally runs fine. Just don't trust the fuel gauge for that tank, and refuel early based on distance driven.

What most often causes P01B1?

Most often it is a failed level sensor or damaged or corroded wiring and connectors. Start by inspecting the connector and measuring the sensor resistance.

Will the code go away on its own?

If it was caused by a momentary poor connection, it may not return. With a real sensor or wiring fault, it will come back until the problem 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.