Damaged, chafed or corroded wiring to the alternative fuel rail temperature sensor; Poor connection at the sensor plug or control unit connector (corrosion, loose pins, moisture); Faulty alternative fuel rail temperature sensor; Short to earth, short to supply or open circuit in the sensor signal or reference wiring; Fault in the alternative fuel control unit or engine control unit; Poorly fitted aftermarket or conversion wiring on a converted vehicle.

P01B4

Alternative Fuel Rail Temperature Sensor Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
B4: FaultThe specific fault in that area

What it means

P01B4 is a generic code for a fault in the circuit of the alternative fuel rail temperature sensor, used on bi-fuel or dual-fuel systems such as LPG or CNG alongside petrol. The control unit has seen a signal from the sensor that is out of its expected range, or a reading that does not make sense. Which fuel system and which sensor it refers to depends on the model and conversion, so check the manufacturer's information for the vehicle.

Symptoms

Engine warning light on
Poor starting or long cranking when running on the alternative fuel
Car stays on petrol or switches fuel unexpectedly
Rough running, hesitation or reduced power on the alternative fuel
Higher fuel consumption or poor economy

Possible causes

Damaged, chafed or corroded wiring to the alternative fuel rail temperature sensorlikely
Poor connection at the sensor plug or control unit connector (corrosion, loose pins, moisture)likely
Faulty alternative fuel rail temperature sensorlikely
Short to earth, short to supply or open circuit in the sensor signal or reference wiringpossible
Fault in the alternative fuel control unit or engine control unitrare
Poorly fitted aftermarket or conversion wiring on a converted vehiclepossible

How to diagnose

Read all stored codes and freeze frame data, noting which fuel was in use and the engine temperature when the code set.
Check for other fuel system or sensor supply codes that point to a shared wiring or power fault.
Visually inspect the sensor, its wiring and connectors for damage, heat, rubbing, corrosion or water.
With a scan tool, view the live sensor reading and compare it to a similar ambient or coolant temperature on a cold engine.
Wiggle the harness and connector while watching the live reading for dropouts or jumps.
Using the wiring diagram for the model, test the sensor supply, signal and earth with a multimeter, and check for shorts or open circuits.
Measure the sensor resistance and compare it with the manufacturer's temperature specification.
Clear the code after repair and road test on the alternative fuel to confirm it does not return.

How to fix

Repair or replace damaged wiring and ensure it is routed and secured away from heat and sharp edges.
Clean or replace corroded or loose connectors and terminals.
Replace the alternative fuel rail temperature sensor if it is out of specification.
Correct any faulty conversion or aftermarket wiring to the manufacturer's or installer's specification.
Where tests show the control unit is at fault, repair or replace it and have it programmed as required.

Can I keep driving?

Medium severity

The car can usually be driven on petrol in the short term, but get it checked soon as the alternative fuel system may not run correctly. Stop driving if it runs very roughly or you smell fuel or gas.

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