What does code P21A4 mean?

Q: What does code P21A4 mean?

Cylinder 9 Air-Fuel Ratio Imbalance. P21A4 indicates that the powertrain control module has detected an air-fuel ratio imbalance on cylinder 9, meaning that cylinder's combustion is not matching the fuel and air delivery of the other cylinders. The computer monitors crankshaft speed fluctuations and oxygen sensor feedback to flag this cylinder as contributing to an overall rich or lean condition.

DTC codes / P21xx · Fuel and air metering / P21A4

P21A4Cylinder 9 Air-Fuel Ratio Imbalance

P21A4 indicates that the powertrain control module has detected an air-fuel ratio imbalance on cylinder 9, meaning that cylinder's combustion is not matching the fuel and air delivery of the other cylinders. The computer monitors crankshaft speed fluctuations and oxygen sensor feedback to flag this cylinder as contributing to an overall rich or lean condition.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.