Faulty or slow-responding alternative fuel rail temperature sensor; Damaged wiring, poor connection or corroded terminals at the sensor or connector; Sensor contaminated, loose or poorly mounted so it does not read true rail temperature; Fault in the alternative fuel system or its controller affecting the reading, such as a heat-related or flow issue; Incorrect or faulty aftermarket conversion wiring or installation, depending on the vehicle; Engine control unit fault or outdated calibration, where a known issue is documented for that model.

P01B5

Alternative Fuel Rail Temperature Sensor Performance.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
B5: FaultThe specific fault in that area

What it means

P01B5 is a generic powertrain code meaning the alternative fuel rail temperature sensor signal does not behave as the control unit expects. The engine control unit compares the reading with other data, such as engine coolant or intake air temperature after a cold soak, or looks for a signal that is slow, stuck or drifting. Which fuel this applies to (for example LPG, CNG or a second fuel) and where the sensor sits depends on the vehicle and conversion.

Symptoms

Engine warning light on
Hard or extended starting on the alternative fuel
Rough running or hesitation on the alternative fuel
Car switching back to petrol or the primary fuel unexpectedly
Poor fuel economy or reduced power
No noticeable change in driveability

Possible causes

Faulty or slow-responding alternative fuel rail temperature sensorlikely
Damaged wiring, poor connection or corroded terminals at the sensor or connectorlikely
Sensor contaminated, loose or poorly mounted so it does not read true rail temperaturepossible
Fault in the alternative fuel system or its controller affecting the reading, such as a heat-related or flow issuepossible
Incorrect or faulty aftermarket conversion wiring or installation, depending on the vehiclepossible
Engine control unit fault or outdated calibration, where a known issue is documented for that modelrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including coolant and intake air temperature and engine run time.
Check for related codes covering the alternative fuel system, other temperature sensors or the sensor circuit, and deal with those first.
Inspect the sensor, wiring and connector for damage, chafing, heat damage, corrosion, water ingress and security of mounting.
After a long cold soak, compare the alternative fuel rail temperature reading with coolant and intake air temperature on live data; they should be close.
Watch the reading as the engine warms up and check it rises smoothly without jumps, dropouts or a stuck value.
Measure sensor resistance and circuit voltage and compare with the manufacturer's specification for that vehicle.
Check the wiring for continuity and for short to earth or supply between the sensor and the control unit.
Check for any manufacturer service information or software updates relating to this code for the specific model.

How to fix

Replace the alternative fuel rail temperature sensor if its readings are out of specification or erratic.
Repair or replace damaged wiring, connectors or terminals, and clear any contamination.
Refit or secure the sensor correctly so it senses true rail temperature.
Correct any fault in the alternative fuel system or conversion installation that is causing an implausible reading.
Update the control unit calibration only where the manufacturer lists an outdated or faulty calibration as a known cause.

Can I keep driving?

Low severity

The car can usually be driven and will normally run on its primary fuel, but book it in soon. If the car runs poorly or the alternative fuel system behaves oddly, have it checked sooner.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.