What it means
Fuel control system B on bank 2 has detected a lean condition at higher load. The code identifies the operating condition and fuel control system; it does not establish a turbocharger or charge-air system.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Fuel control system B monitors mixture correction for bank 2. The module evaluates that bank’s mixture feedback at higher engine load and sets P21FE when it indicates too little fuel for the air entering; the code alone does not identify a particular leak or failed part.
Common causes
Most likely first.
- Low fuel pressure or restricted fuel supply
- Fuel injector under-delivery on bank 2
- Air leak or unmetered air affecting bank 2
- Faulty air-fuel or oxygen sensor
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
How to diagnose it
- Read freeze-frame data and fuel trims to confirm the lean event occurred at higher load and determine whether correction is concentrated on bank 2.
- Inspect bank 2 intake connections, vacuum hoses, and nearby wiring for leaks or damage that could introduce unmetered air or corrupt sensor readings.
- Compare bank 2 mixture sensor readings with bank 1 during a controlled load increase to check whether the abnormal response is limited to bank 2.
- Measure fuel pressure during load and compare it with the manufacturer’s specification; inspect for restricted supply if pressure falls.
- Test bank 2 injector delivery and check the air-fuel or oxygen sensor signal against the actual mixture before replacing parts.
Common fixes
- Seal a confirmed air leak affecting bank 2.
- Replace a restricted fuel filter or repair a fuel supply fault causing low pressure under load.
- Clean or replace an under-delivering bank 2 injector.
- Repair wiring or replace a bank 2 mixture sensor if testing confirms an inaccurate signal.
Can I keep driving?
Avoid heavy acceleration, towing, and long journeys because the engine may hesitate or lose power under load and could stall. Stop if it misfires or the power loss makes driving unsafe.
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.