OBD-II code · Powertrain (generic, extended)
P21F8 Fuel Control System B Too Lean at Idle (Bank 1)
Secondary fuel control loop B reports a lean condition at idle on bank 1. Idle is sensitive to vacuum leaks since manifold flow is low.
Is it safe to drive with P21F8?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyVacuum leak — most visible at idle
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.7–3.5 h
- Emissions test
- Likely to fail
- Parts involved
- Fuel Injector, Intake Manifold, Oxygen Sensor
Related codes
- P21F4Fuel Control System B Too Lean Off Idle (Bank 1)
- P21FAFuel Control System B Too Lean at Idle (Bank 2)
- P21F5Fuel Control System B Too Rich Off Idle (Bank 1)
- P21F6Fuel Control System B Too Lean Off Idle (Bank 2)
- P21F7Fuel Control System B Too Rich Off Idle (Bank 2)
- P21F9Fuel Control System B Too Rich at Idle (Bank 1)
- P21FBFuel Control System B Too Rich at Idle (Bank 2)
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.