Powertrain
generic / SAE
P21F4
Fuel Control System B Too Lean Off Idle (Bank 1)
The secondary fuel control loop B on bank 1 reports a lean condition outside idle. On dual-injection systems (port + direct) the secondary loop trims port injection independently from the main loop.
SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number1 / F4
Possible causes
- Vacuum leak high
- Port injectors clogged medium
- Fuel pressure low medium
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
Inspection / repair
- Difficulty: medium
- DIY: possible
- Estimated cost: 80–1000 €
- Estimated time: 0.7–4 h
- Component: fuel injector
- Component: fuel pressure regulator
- Component: oxygen sensor
- MIL / check engine light
- emissions-relevant
Sources
References
sae:J2012