Code result
P21F4
Fuel Control System B Too Lean Off Idle
Moderate severity
What it means
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.
Is it safe to drive?
Use caution
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical.
Most likely causes
Vacuum leak
highOne of the most commonly reported causes for this code — check this first.
Port injectors clogged
mediumA plausible cause — test and verify before replacing parts.
Fuel pressure low
mediumA plausible cause — test and verify before replacing parts.
Related help
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