What it means
The outlet temperature signal of alternative fuel vaporizer A does not match plausibility checks against fuel rail temperature and engine coolant temperature. Sensor drift.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The outlet-temperature sensor on alternative fuel vaporizer A reports the temperature of fuel leaving that vaporizer to the AFCM. The AFCM compares that reading with fuel-rail and engine-coolant temperatures; this code sets when the outlet reading fails those plausibility checks, even if the circuit is electrically intact.
Common causes
Most likely first.
- Sensor characteristic drifted
- Sensor mounting displaced from fluid path
- Sensor element aged beyond calibration window
Symptoms
- Check-engine or alternative-fuel system warning light
- Rough running or hesitation on alternative fuel
- Reduced fuel economy
How to diagnose it
- Record freeze-frame data and compare vaporizer A outlet temperature with fuel-rail and coolant readings under the conditions that set P2A51.
- With the engine cold, compare the three temperature readings and watch their changes during warm-up for a vaporizer A value that drifts or responds implausibly.
- Inspect the vaporizer A sensor mounting to confirm the sensing element is properly positioned in the outlet flow path.
- Check the vaporizer A sensor and connector for damage or contamination, and inspect its wiring for faults that could distort the signal.
- If mounting and wiring are sound, test the sensor's temperature response against the manufacturer's specification and replace it if it has drifted.
Common fixes
- Secure the vaporizer A outlet-temperature sensor in its intended position in the fuel path.
- Clean or repair the vaporizer A sensor connector and wiring if inspection finds a fault.
- Replace the vaporizer A outlet-temperature sensor if its readings fail the manufacturer's temperature-response specification.
Can I keep driving?
If the engine runs smoothly, a short trip may be possible, but avoid relying on alternative-fuel operation if hesitation develops. Incorrect vaporizer A temperature feedback can reduce fuel economy and increase emissions.
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.