What it means
On bi-fuel vehicles, the AFCM cannot transition into alternative fuel control mode within the calibrated time window. Tank pressure low, vaporizer cold, or fuel quality limits the change-over.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The AFCM controls the change from gasoline to alternative fuel on a bi-fuel vehicle. It monitors whether conditions such as alternative-fuel tank pressure and vaporizer temperature allow the system to enter alternative-fuel control within its calibrated time. P2A3F sets when that transition takes too long, so the engine may continue running on gasoline.
Common causes
Most likely first.
- Alt fuel tank pressure low
- Vaporizer not yet at operating temperature
Symptoms
- Check-engine light
- Delayed switch to alternative fuel
- Unexpected continued operation on gasoline
How to diagnose it
- Use a scan tool to capture freeze-frame data and check AFCM live data for the requested fuel mode, transition status, tank pressure, and vaporizer temperature.
- Confirm the alternative-fuel tank has adequate fuel and that low pressure is not preventing the changeover.
- Check whether the vaporizer has reached its specified operating temperature before the transition is requested.
- Inspect the alternative-fuel pressure-sensing and vaporizer-temperature wiring and connectors for damage or poor contact.
- If pressure and temperature conditions appear normal, test the relevant sensors and changeover controls against the manufacturer’s specification.
Common fixes
- Refill the alternative-fuel tank if its level or pressure is too low for changeover.
- Repair a loose or damaged pressure-sensor or vaporizer-temperature connection.
- Repair the vaporizer heating or temperature-control fault if it prevents the unit reaching operating temperature.
- Replace a pressure or temperature sensor only if it fails the specified tests.
Can I keep driving?
The vehicle may continue on gasoline, so the immediate driving effect can be limited if gasoline operation is normal and available. Do not rely on alternative-fuel range or changeover until the fault is diagnosed, and stop if the engine hesitates or loses power.
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.