What it means
The control module checks whether the alternative fuel rail temperature sensor reading is plausible under current operating conditions. It sets this code when the reading is outside the expected range or does not respond as expected.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The alternative fuel rail temperature sensor tells the control module how warm the fuel in the rail is. The module checks whether that reading is plausible and responds as operating conditions change; P01B5 sets when the reading is out of range or does not respond as expected.
Common causes
Most likely first.
- Sensor reading drifted
- Sensor element aged beyond calibration window
- Sensor element contaminated by oil, soot or coolant
Symptoms
- Check-engine light on
- Alternative-fuel rail temperature reading may be inaccurate or unavailable
- Poor running or reduced power may occur
How to diagnose it
- Save freeze-frame data and compare the reported rail temperature with the conditions when the code set to identify an implausible reading.
- Watch live rail temperature data from a cold start through normal operation and note whether it changes smoothly and plausibly.
- Inspect the alternative fuel rail temperature sensor and connector for contamination, damage, looseness, or corrosion.
- Check the sensor wiring and connector for sound signal, supply, and ground connections using the manufacturer's procedure.
- Test the rail temperature sensor against the manufacturer's specification and replace it if its response is inaccurate.
Common fixes
- Clean contamination from the sensor if the manufacturer's service procedure permits it.
- Repair a loose, damaged, or corroded rail temperature sensor connector or wiring.
- Replace the alternative fuel rail temperature sensor if its reading is outside the manufacturer's specification.
Can I keep driving?
The code can be accompanied by poor running or reduced power if the alternative-fuel system receives an unreliable rail temperature reading. Drive gently and avoid heavy loads if performance is affected; arrange diagnosis soon.
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.