Fuel and air

P01B5 — Alternative Fuel Rail Temperature Sensor Performance

Severity: medium Drive with care, to a shop

What P01B5 means

P01B5 means the engine control module found that the signal from the fuel rail temperature sensor on the secondary fuel system (such as CNG or LPG) does not match what it expects. The ECM uses fuel temperature to estimate fuel density and calculate delivery accurately. The signal may not be missing outright; it can be stuck, erratic, or slow to change as the engine warms up.

Symptoms

  • Check Engine Light on
  • Rough or unstable idle
  • Worse fuel economy
  • Misfires or hesitation
  • Reduced power
  • Switching to gasoline or hard starting on the alternative fuel

Possible causes

  1. Failed fuel rail temperature sensor
  2. Damaged wiring: open, short to power or short to ground
  3. Corroded or loose connector causing high resistance
  4. A fuel system fault pushing actual temperature out of range
  5. ECM software issue (uncommon)

How to diagnose

  1. Read all codes and freeze frame data, note the conditions, clear the code and see if it returns
  2. Inspect the sensor, connector and harness for chafing, moisture, corrosion or heat damage
  3. With a scan tool, compare fuel rail temperature to coolant and intake air temperature on a cold engine; they should be close
  4. Watch the reading while the engine warms up for jumps, freezing or unrealistic values
  5. Use a multimeter to check reference voltage, ground and sensor resistance against the manufacturer's specs
  6. Test the wiring to the ECM for opens and shorts
  7. Check alternative fuel system pressure and operation
  8. Look for ECM software updates or service bulletins for your vehicle

Common fixes

  • Replace the fuel rail temperature sensor
  • Repair the wiring or replace the damaged connector and clean the terminals
  • Fix any fuel system fault affecting rail temperature
  • Update or reflash the ECM if the manufacturer offers a fix

Questions and answers

What does P01B5 mean?

The ECM thinks the alternative fuel rail temperature sensor signal is out of line with expected values. The sensor itself or its wiring is the most common culprit.

Can I drive with P01B5?

Usually yes for short trips, possibly on gasoline. Don't put it off, though, since the engine may run rough and use more fuel.

How do I fix P01B5?

Start by inspecting the connector and wiring, then test the sensor with a multimeter and scan tool. If the wiring is good, replace the 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.