What it means
Alt fuel tank temp sensor signal voltage below expected range. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The alternative-fuel tank temperature sensor sends a voltage signal representing tank temperature to the control module. P01AC means the signal is below the expected electrical range, which can result from a signal wire shorted to ground or damaged wiring.
Common causes
Most likely first.
- Signal wire shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check-engine light on
- Alternative-fuel tank temperature reading may be inaccurate or unavailable
- Alternative-fuel system warning may appear
How to diagnose it
- Record freeze-frame data and check the live tank temperature reading for an implausible value that accompanies the low signal.
- Inspect the temperature sensor connector and harness for chafing, moisture, corrosion, and contact with grounded metal.
- Move the harness gently while monitoring the reading to see whether the low signal changes.
- Check the sensor signal wire for a short to ground and inspect connector terminals for corrosion or poor contact.
- Test the sensor and circuit against the manufacturer's specification after ruling out wiring damage.
Common fixes
- Repair insulation damage where the signal wire is shorted to ground.
- Clean or replace corroded connector terminals.
- Secure or reroute the harness to prevent renewed chafing.
- Replace the tank temperature sensor if its output remains out of range with a sound circuit.
Can I keep driving?
If the vehicle runs normally, drive only as needed and monitor for alternative-fuel warnings or changes in operation. The tank temperature reading may be unreliable; stop if the system warning escalates or the engine runs abnormally.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.