Fuel and air

P01B7 — Alternative Fuel Rail Temperature Sensor Circuit High

Severity: medium Drive with care, to a shop

What P01B7 means

The engine control module detected a voltage from the alternative fuel rail temperature sensor (such as CNG, LPG or ethanol systems) that is higher than expected. This usually points to an open circuit, a poor connection or a failed sensor. The module uses rail temperature to adjust alternative fuel delivery, so the calculation can be off when the signal is wrong.

Symptoms

  • Check engine light on
  • Reduced engine power
  • Poor fuel economy
  • Rough running or hesitation
  • Engine switches to primary fuel (gasoline)
  • Hard starting on alternative fuel

Possible causes

  1. Failed fuel rail temperature sensor
  2. Open signal wire or poor connector contact
  3. Corroded or dirty connector terminals
  4. Open or lost sensor ground
  5. Signal wire shorted to power
  6. Truly overheated fuel rail
  7. Rarely, a faulty PCM or gas control module

How to diagnose

  1. Read all codes and freeze frame data, clear the code and see if it returns.
  2. Inspect the sensor, connector and harness for damage, heat marks, corrosion and moisture.
  3. With a scan tool, compare the rail temperature reading to actual temperature; on a cold engine it should be near ambient.
  4. Unplug the connector and check for reference voltage (usually about 5 V) and ground per the wiring diagram.
  5. Measure the sensor resistance and compare it to the spec for its temperature.
  6. Test the signal wire for opens and shorts to power between the sensor and the module.
  7. Confirm the rail is not actually overheated, for example with an infrared thermometer.
  8. Try a known good sensor and watch the reading.

Common fixes

  • Replace the fuel rail temperature sensor
  • Repair or replace the damaged wiring or connector
  • Clean the terminals and restore the ground connection
  • Fix the cause of rail overheating
  • Update software or replace the module if everything else checks out

Questions and answers

What does P01B7 mean?

The engine module sees a signal that is too high in the alternative fuel rail temperature sensor circuit. The sensor or its wiring is the most common cause.

Can I drive with P01B7?

Usually yes, carefully: expect possible power loss and higher fuel use. Do not put off diagnosis, especially if you smell gas.

How do I fix P01B7?

Check the connector and wiring, then measure sensor voltage and resistance. If the circuit is good, replace the sensor and clear the code.

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.