P21FC
Fuel Control System B Too Lean at Higher Load (Bank 1)
Secondary fuel control loop B on bank 1 reports a lean condition at higher load. Lean at high load typically points at fuel pressure shortfall, restricted injectors, or charge-air leak.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
Common causes
Ordered by how often each turns out to be the cause.
- Fuel pressure drops under loadCommon
- Charge-air leak after turboPossible
Parts involved
- Fuel Pressure Regulator
- Fuel Injector
- Charge Air Pipe
P21FC is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.