P21A0
Cylinder 5 Air-Fuel Ratio Imbalance
What it means
P21A0 means Cylinder 5 Air-Fuel Ratio Imbalance.
Check these first
- A dirty or faulty fuel injector on cylinder 5
- A weak spark plug on cylinder 5
- An intake manifold leak near cylinder 5
- Low compression on cylinder 5
- A fuel pressure or fuel temperature sensor fault
What to do next
- Read the cylinder 5 fuel trim on a scan tool
- Swap the cylinder 5 injector and see if the fault follows
- Check the cylinder 5 spark plug
- Check for an intake leak near cylinder 5
- Run a compression test on cylinder 5
- Clear the code and retest
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Updated
Generic SAE J2012 definition. Last updated 2026-10-10.