Fuel and air

P01B6 — Alternative Fuel Rail Temperature Sensor Circuit Low

Severity: medium Drive with care, to a shop

What P01B6 means

The PCM monitors fuel temperature in the alternative fuel rail (such as gaseous fuel or ethanol blends) using a thermistor sensor whose signal voltage changes with temperature. P01B6 sets when that voltage stays below the expected range, usually from a short to ground or a failed sensor. Without a valid reading, the PCM cannot adjust fuel delivery accurately.

Symptoms

  • Check engine light on
  • Reduced fuel economy
  • Hesitation or stumbling under acceleration
  • Rough idle
  • Hard starting, especially on alternative fuel
  • Incorrect fuel trim adjustments

Possible causes

  1. Failed fuel rail temperature sensor
  2. Signal wire shorted to ground from damaged insulation
  3. Corroded or damaged sensor connector
  4. Moisture in the connector
  5. Faulty 5 V reference or internal PCM circuit (rare)

How to diagnose

  1. Scan for codes and freeze frame data, clear the code and see if it returns
  2. Check live data for fuel rail temperature: an implausible or frozen value points to the circuit
  3. Inspect the sensor, connector and harness for chafing, moisture and corrosion
  4. Unplug the sensor: if the reading goes to an open-circuit value, the sensor or wiring after the connector is at fault
  5. Measure the 5 V reference and ground at the connector
  6. Test the signal wire for a short to ground and for opens
  7. Measure sensor resistance and compare to spec at a known temperature
  8. If wiring and sensor are good, test the PCM

Common fixes

  • Replace the fuel rail temperature sensor
  • Repair or replace the damaged wiring harness section
  • Clean or replace the connector
  • Diagnose and repair or replace the PCM (last resort)

Questions and answers

What does P01B6 mean?

It means the alternative fuel rail temperature sensor circuit has a low voltage signal. The PCM cannot read fuel temperature correctly.

Can I drive with P01B6?

Briefly, yes, but fuel delivery may be inaccurate, hurting performance and economy. Get it diagnosed soon.

How do I fix P01B6?

Check the connector and wiring for a short to ground first, then the sensor. If both are good, the PCM needs testing.

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.