P01AC: Alternative Fuel Tank Temperature Sensor Circuit Low

What does P01AC mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

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

Common causes

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

Likelihood is a general estimate across vehicles; your make and model may differ.