P01AC: Alternative Fuel Tank Temperature Sensor Circuit Low

These codes only apply to vehicles with a gaseous alternative fuel – compressed natural gas (CNG) or LPG – as bi-fuel models alongside petrol or as dedicated gas engines; on bi-fuel vehicles a fault usually blocks gas operation and the vehicle runs on petrol. The tank temperature sensor is an NTC thermistor: with CNG there is no float, so the gas level is calculated from tank pressure and tank temperature (GM: full at about 3600 psi at 21 °C, empty at about 400–500 psi). On GM's 2015 Impala Bi-Fuel the sensor is built into the tank and cannot be replaced separately. P01AC means the signal voltage is too low – with an NTC an apparently very hot tank, typically a signal wire shorted to ground or an internally shorted sensor. The Roush propane conversion for Ford E- and F-series trucks (2016–2018) uses this code for its combined tank pressure/temperature sensor (NTC, 8–12 kΩ at 20–30 °C), with the signal travelling via its own module and CAN to the engine module; according to its table the code does not light the MIL.

High severity. Can I keep driving?If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.

Symptoms

Stored fault code (warning light depending on system)
Gas level display wrong
Gas operation blocked, switch to petrol

Most likely causes

Signal wire shorted to ground
Sensor shorted internally
Moisture or corrosion in the connector
Gas or engine module

What to check, in order

Start with the simplest. You can tick off each step.

If you smell gas, shut off the supply, ventilate and do not start the engine
With the connector unplugged, check whether the signal wire is making contact with ground.
Read the codes with a compatible scanner
Check the connectors and wiring of the component indicated
Leave any work on the gas circuit to an authorized shop

Good to know

Repair difficulty: hard
It can trigger limp mode.
It affects emissions.

What each character of P01AC means

P: Powertrain: engine and transmission
0: Generic code: same on every make
1: Air and fuel
AC: Specific fault in that system

Frequently asked questions

Can I keep driving with code P01AC?

If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.

What causes code P01AC?

The most common causes are: signal wire shorted to ground; sensor shorted internally; moisture or corrosion in the connector.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.