P01AC code meaning
Alternative Fuel Tank Temperature Sensor Circuit Low
What P01AC means
These codes only apply to vehicles with a gaseous alternative fuel – compressed natural gas (CNG) or LPG – as bi-fuel models alongside gasoline or as dedicated gas engines; on bi-fuel vehicles a fault usually blocks gas operation and the vehicle runs on gasoline. 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.
P01AC at a glance
- Check engine lightUsually not
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of P01AC
- Stored fault code (warning light depending on system)
- Gas level display wrong
- Gas operation blocked, switch to gasoline
Common causes of P01AC
- Most likelySignal wire shorted to ground
- PossibleSensor shorted internally
- PossibleMoisture or corrosion in the connector
- Less likelyGas or engine module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Alternative fuel tank temperature sensorSensor wiring
What each part of P01AC means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 1 | Area: fuel and air metering. |
| AC | The exact fault in that area. |
What to do next
- Note P01AC and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P01AC
What does P01AC mean?
P01AC means "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 gasoline or as dedicated gas engines; on bi-fuel vehicles a fault usually blocks gas operation and the vehicle runs on gasoline. It is a generic code, so it means the same on every make.
Is it safe to drive with P01AC?
Drive gently and only to a workshop. With P01AC the car can go into limp mode (reduced power) to protect itself.
Will P01AC fail an emissions test?
Yes, it can. P01AC is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P01AC to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P01AC clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.