What it means
The level signal of alternative fuel tank B does not match plausibility checks against consumption and refuel events. Float stuck or capacitive sensor drift.
At a glance
- Usually lights the check-engine light
How it works
The AFCM checks the level reported by alternative fuel tank B against fuel consumption and refuelling events. This range/performance code sets when the reported level does not change or behave plausibly, which can happen if the float sticks or the sensor has drifted.
Common causes
Most likely first.
- Float stuck on guide rod
- Sensor characteristic drifted
- Sensor element aged beyond calibration window
Symptoms
- Check-engine or alternative-fuel system warning light
- Alternative-fuel tank level or remaining range may be inaccurate
- Fuel gauge reading may fluctuate
How to diagnose it
- Review freeze-frame and AFCM level data alongside recent refuelling and consumption history to identify how tank B's reading became implausible.
- Compare the tank B level display with the known refuelling amount and observe whether the reading changes plausibly after refuelling.
- Inspect the sensor connector and accessible wiring for poor connections that could make the level fluctuate.
- Following the vehicle's service information, check whether the tank B float moves freely on its guide rod or whether the sensor is correctly positioned.
- If the float and wiring are sound, test the level sensor against the manufacturer's specification for drift or an aged sensing element.
Common fixes
- Free a tank B level-sensor float that is sticking on its guide rod.
- Correct a displaced sensor or poor connector that is affecting the reading.
- Repair damaged tank B sensor wiring or terminals.
- Replace a tank B level sensor that has drifted out of specification.
Can I keep driving?
You can generally drive if the vehicle runs normally, but treat the tank B gauge and range estimate as unreliable and refuel early. A stuck or drifting reading could leave you short of alternative fuel without warning.
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.