P231C
Cylinder 9 Air-Fuel Ratio Imbalance Adjustment At Limit During Balance
What it means
The ECU continuously trims individual cylinders to equalise air-fuel ratio across the bank using ion-current or per-cylinder lambda feedback. For cylinder 9 the per-cylinder fuel correction has hit its software-side maximum or minimum without restoring balance, indicating the underlying mechanical or fuelling deviation is too large to compensate.
Is it safe to drive?
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
Fuel injector for cylinder 9 has drifted in flow rate
highOne of the most commonly reported causes for this code — check this first.
Reduced compression on cylinder 9
mediumA plausible cause — test and verify before replacing parts.
Related help
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