Signal wire chafed or shorted to ground near the tank or along the harness; Faulty alternative fuel tank temperature sensor with an internal short; Water or corrosion in the sensor connector pulling the signal low; Damaged or poorly fitted connector terminals at the tank or control unit; Fault in a separate alternative fuel control unit or its wiring where fitted; Internal fault in the engine control unit input circuit.

P01AC

Alternative Fuel Tank Temperature 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
AC: FaultThe specific fault in that area

What it means

P01AC means the engine control unit has seen the signal from the alternative fuel tank temperature sensor drop below its expected range, which points to a low-voltage or short-to-ground condition. This applies to vehicles running an alternative fuel such as LPG or CNG, often alongside petrol. The control unit uses tank temperature to work out fuel density and delivery, so a signal that is too low is treated as a circuit fault.

Symptoms

Engine warning light on
Car may refuse to run on the alternative fuel or switch back to petrol
Poor fuel economy on the alternative fuel
Rough running, hesitation or poor power on gas
Alternative fuel gauge or level reading incorrect or unavailable

Possible causes

Signal wire chafed or shorted to ground near the tank or along the harnesslikely
Faulty alternative fuel tank temperature sensor with an internal shortlikely
Water or corrosion in the sensor connector pulling the signal lowpossible
Damaged or poorly fitted connector terminals at the tank or control unitpossible
Fault in a separate alternative fuel control unit or its wiring where fittedpossible
Internal fault in the engine control unit input circuitrare

How to diagnose

Read all stored and pending codes and note any other alternative fuel or sensor supply faults, then review the freeze frame data.
Check live data for the alternative fuel tank temperature and see whether it reads implausibly cold or fixed at the lowest value.
Visually inspect the sensor, connector and harness near the tank for chafing, crush damage, moisture and corrosion.
With the connector unplugged, see if the reading changes in live data, which helps separate a sensor fault from a wiring short.
Measure the sensor resistance and compare it with the specification for that vehicle and tank type, as values vary by model and system.
Check the reference voltage and signal wire for a short to ground and the ground circuit for good continuity, using the wiring diagram for the vehicle.
Wiggle test the harness with live data showing to find intermittent faults.
Check whether the sensor is a separate part or built into the tank valve assembly, as this depends on the vehicle and conversion.

How to fix

Repair or replace any damaged wiring and secure it away from sharp edges and heat.
Clean, dry and repair or replace corroded or damaged connectors and terminals.
Replace the tank temperature sensor or the assembly it is part of if it tests out of specification.
Repair or replace the alternative fuel control unit or engine control unit only after wiring and sensor have been proven good.
Clear the codes after repair and road test to confirm the fault does not return.

Can I keep driving?

Low severity

The car can usually be driven, often on petrol only, while you book it in for repair. If you smell gas or notice any leak, stop and have the system checked by a qualified person before further use.

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