Damaged, corroded or loose wiring or connector at the tank level sensor; Faulty alternative fuel tank level sensor or sender; Open circuit, short to earth or short to supply in the sensor signal, supply or earth wires; Water ingress or contamination in the sensor connector or tank fitting; Fault in a separate alternative fuel control unit that processes the level signal (depends on system); Fault in the engine control unit or its software calibration (only if a known issue exists for the model).

P01AF

Alternative Fuel Tank A Level Sensor Circuit.

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
AF: FaultThe specific fault in that area

What it means

P01AF is a generic code for a fault in the Alternative Fuel Tank A Level Sensor circuit. The control unit monitors the signal from the level sensor in the secondary fuel tank, such as a bi-fuel LPG or CNG system. It has seen a voltage or signal outside the expected range, or one that does not make sense, so it cannot trust the reported fuel level. The exact fault limits and how the sensor is wired depend on the vehicle and the alternative fuel system.

Symptoms

Alternative fuel gauge reads empty, full or stuck, or jumps about
Warning light on (engine management or alternative fuel system)
Car refuses to run on, or switches back to petrol early from, the alternative fuel
Unexpected changeover between fuels, or no changeover at all
Incorrect range or low fuel warnings for the alternative fuel

Possible causes

Damaged, corroded or loose wiring or connector at the tank level sensorlikely
Faulty alternative fuel tank level sensor or senderlikely
Open circuit, short to earth or short to supply in the sensor signal, supply or earth wirespossible
Water ingress or contamination in the sensor connector or tank fittingpossible
Fault in a separate alternative fuel control unit that processes the level signal (depends on system)rare
Fault in the engine control unit or its software calibration (only if a known issue exists for the model)rare

How to diagnose

Read all stored and pending codes and the freeze frame data, and note whether other fuel system or alternative fuel codes are present.
Check the fuel level reading from the alternative fuel tank on a scan tool and see whether it is fixed, erratic or out of range.
Inspect the wiring and connectors from the tank sensor to the control unit for chafing, corrosion, water, bent pins and loose fits.
Check the sensor supply voltage, reference and earth at the connector against the manufacturer's data.
Measure the sensor signal while the level changes or the sensor is moved, if safe and permitted, and check its resistance or voltage against specification.
Test the signal wire for continuity and for shorts to earth or supply, with the connector unplugged at both ends.
Check for any technical service information or calibration updates for the model and alternative fuel system.
Clear the code after repair and road test, then recheck for the code returning.

How to fix

Repair or replace damaged wiring and clean or replace corroded or damaged connectors.
Replace the alternative fuel tank level sensor if it is out of specification, following safe procedures for the fuel type.
Restore correct supply, earth and signal circuit integrity by repairing open or shorted wires.
Dry and seal connectors that have water ingress and fix the source of the leak.
Repair or replace the alternative fuel control unit if testing shows it is faulty, or update its calibration if an update exists for a known fault.

Can I keep driving?

Low severity

The car can normally be driven, usually on petrol only, as the fault mainly affects the alternative fuel level reading. Book it in soon, as you may lose the alternative fuel operation or have no reliable level indication. Work on alternative fuel tanks should be left to a qualified person.

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