OBD
P21A7
Cylinder 12 Air-Fuel Ratio Imbalance
What it means
P21A7 means Cylinder 12 Air-Fuel Ratio Imbalance.
Check these first
- A dirty mass airflow sensor
- A weak oxygen sensor
- A dirty or faulty fuel injector on cylinder 12
- An intake manifold or exhaust leak
- Low compression on cylinder 12
What to do next
- Read the cylinder 12 fuel trim on a scan tool
- Swap the cylinder 12 injector and see if the fault follows
- Clean the mass airflow sensor
- Check for intake and exhaust leaks
- Run a compression test on cylinder 12
- Clear the code and retest
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Updated
Generic SAE J2012 definition. Last updated 2026-10-10.