What it means
Alt fuel rail 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 rail temperature sensor sends the control module an electrical signal representing rail temperature. P01B6 sets when the signal voltage falls below the expected range, which can occur if the signal wire is grounded or the connection has excessive resistance.
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 rail temperature reading may be inaccurate or unavailable
- Poor running or reduced power may occur
How to diagnose it
- Save freeze-frame data and check whether rail temperature data is implausibly low or unavailable while the fault is active.
- Inspect the rail temperature sensor connector and harness for chafing, water intrusion, corrosion, pushed-back pins, or a signal wire touching ground.
- Monitor rail temperature data while gently moving the accessible sensor harness to see whether the low reading changes.
- Using the manufacturer's wiring information, check the signal circuit for a short to ground and inspect connector contact quality.
- If the circuit is intact, test the rail temperature sensor and its supply and ground against the manufacturer's specification.
Common fixes
- Clean and secure corroded or loose rail temperature sensor connector pins.
- Repair chafed sensor wiring that is shorted to ground.
- Replace the rail temperature sensor if it fails the manufacturer's electrical test.
Can I keep driving?
An unreliable rail temperature signal can affect alternative-fuel operation and may cause poor running or reduced power. Avoid heavy loads if performance is affected and arrange prompt diagnosis.
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.