Level sensor signal wire shorted to ground or chafed against bodywork; Corroded, wet or damaged connector at the tank or the control unit; Faulty tank level sensor or sender, often part of the tank valve assembly on many systems; Open circuit or high resistance in the sensor reference or signal wiring causing a low reading; Poor sensor earth connection or low supply voltage to the gas control unit; Fault inside the gas control unit or gauge driver.

P01B1

Alternative Fuel Tank A Level Sensor Circuit Low.

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
B1: FaultThe specific fault in that area

What it means

P01B1 means the control unit monitoring the alternative fuel system (for example LPG or CNG) saw the signal from the Alternative Fuel Tank A level sensor drop below its expected range. This is usually a low voltage or short to ground on the sensor circuit, or a sensor reading below its lowest valid value. The exact signal design and thresholds depend on the vehicle and gas system.

Symptoms

Warning light on, possibly with a gas system fault indicator
Alternative fuel gauge reads empty, stuck or erratic
Car switches to petrol early or will not run on the alternative fuel
Low fuel warning for the alternative fuel shown when the tank is not low
Reduced alternative fuel range or poor fuel switchover behaviour

Possible causes

Level sensor signal wire shorted to ground or chafed against bodyworklikely
Corroded, wet or damaged connector at the tank or the control unitlikely
Faulty tank level sensor or sender, often part of the tank valve assembly on many systemslikely
Open circuit or high resistance in the sensor reference or signal wiring causing a low readingpossible
Poor sensor earth connection or low supply voltage to the gas control unitpossible
Fault inside the gas control unit or gauge driverrare

How to diagnose

Read all stored and pending codes and the freeze frame data, and note any other gas system or supply voltage codes
Compare the displayed alternative fuel level with the actual tank contents to confirm whether the reading is wrong
Inspect the sensor wiring and connectors at the tank and control unit for chafing, water, corrosion, bent pins and loose fit
Check the control unit and sensor supply voltage and earth connections against the manufacturer's data
Measure the sensor reference and signal voltage with the sensor connected, then disconnected, and compare with specification for that model
Check the sensor resistance through its range against specification, as the correct values vary by system
Test the signal wire for a short to ground and for continuity end to end with the harness disconnected
Clear the code, road test on the alternative fuel and recheck that the level reading and code behave correctly

How to fix

Repair or replace damaged wiring and secure it clear of sharp edges and heat
Clean, dry and repair or replace corroded or damaged connectors and terminals
Replace the faulty level sensor or the tank valve assembly that contains it, following the manufacturer's procedure
Restore good earth and supply connections to the sensor and control unit
Replace or repair the control unit only after wiring and sensor faults are ruled out, and only if testing shows it is faulty

Can I keep driving?

Low severity

The car can normally keep being driven, usually on petrol if the system switches over, but the alternative fuel level reading cannot be trusted so watch the real fuel level. Book it in soon, and have any work on the gas system done by a suitably qualified technician.

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