What are the common causes of P231C?

A cylinder 9 fuel injector that cannot balance its air-fuel ratio. A worn spark plug or coil on cylinder 9. Low compression on cylinder 9. A vacuum leak at cylinder 9.

Run a cylinder balance test and read cylinder 9 contribution. Swap the cylinder 9 injector with a known good cylinder and retest. Inspect the cylinder 9 spark plug and coil. Run a compression test on cylinder 9. Repair the cylinder 9 fault found and rerun the balance test. Clear the code and retest.

P231C

Cylinder 9 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance

System: Ignition and misfire (P code)
Lamp: Check Engine Light
Category: Powertrain - Ignition

What it means

P231C means Cylinder 9 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance.

Check these first

A cylinder 9 fuel injector that cannot balance its air-fuel ratio
A worn spark plug or coil on cylinder 9
Low compression on cylinder 9
A vacuum leak at cylinder 9

What to do next

Run a cylinder balance test and read cylinder 9 contribution
Swap the cylinder 9 injector with a known good cylinder and retest
Inspect the cylinder 9 spark plug and coil
Run a compression test on cylinder 9
Repair the cylinder 9 fault found and rerun the balance test
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.