Fuel and air

P01B4 — Alternative Fuel Rail Temperature Sensor Circuit Fault

Severity: medium Drive with care, to a shop

What P01B4 means

The engine control module monitors the fuel rail temperature sensor on alternative fuel systems such as CNG or LPG. P01B4 sets when the sensor signal is out of range or unstable. Without a reliable temperature reading, the PCM cannot accurately calculate fuel density and delivery, so fueling becomes less precise.

Symptoms

  • Check Engine Light on
  • Rough idle
  • Reduced power and sluggish acceleration
  • Worse fuel economy
  • Hard starting or hesitation on alternative fuel
  • Limp mode on some vehicles

Possible causes

  1. Failed fuel rail temperature sensor
  2. Open circuit or short to ground or voltage in the sensor wiring
  3. Corroded or loose connector
  4. Intermittent sensor signal
  5. PCM fault (rare)
  6. Code unused or defined differently on some vehicles

How to diagnose

  1. Scan all codes and freeze frame data and look for related fuel system codes
  2. Inspect the sensor wiring and connector for damage, moisture and corrosion
  3. Compare the scan tool fuel rail temperature on a cold engine with ambient temperature
  4. Measure the reference voltage and ground at the sensor connector
  5. Check sensor resistance against the manufacturer's temperature table
  6. Test the wires to the PCM for opens and shorts, wiggling the harness with the engine running
  7. If the circuit is good, replace the sensor, clear the code and see whether it returns

Common fixes

  • Replace the fuel rail temperature sensor
  • Repair or replace damaged wiring
  • Clean or replace the connector and terminals
  • Update PCM software or replace the PCM if confirmed faulty

Questions and answers

What does P01B4 mean?

It is a circuit fault in the fuel rail temperature sensor on an alternative fuel system. The PCM sees a signal that is out of range or unstable.

Can I drive with P01B4?

Usually yes, carefully. You may notice rough running and higher fuel use, so have it checked soon.

How do I fix P01B4?

Inspect the wiring and connector, then test voltage and sensor resistance. If the sensor is bad, replace it 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.