P21F6
Fuel Control System B Too Lean Off Idle (Bank 2)
The secondary fuel control loop B on bank 2 reports a lean condition outside idle. On dual-injection systems (port + direct) the secondary loop trims port injection independently from the main loop.
- 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.
- Vacuum leak or injector clogCommon
Parts involved
- Fuel Injector
- Oxygen Sensor
P21F6 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.