Cylinder 4 Air-Fuel Ratio Imbalance Adjustment At Limit During Balance
The ECU continuously trims individual cylinders to equalise air-fuel ratio across the bank using ion-current or per-cylinder lambda feedback. For cylinder 4 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.
Affected components
- Fuel injector cyl 4
- Intake manifold
- Cylinder compression
- Per cylinder lambda strategy
Common causes
- High likelihood: Fuel injector for cylinder 4 has drifted in flow rate
- Medium likelihood: Local intake or vacuum leak at cylinder 4
- Medium likelihood: Reduced compression on cylinder 4
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
Related codes
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.