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DTC codes / P23xx · Ignition system and misfire / P231C

P231CCylinder 9 Air-Fuel Ratio Imbalance Adjustment At Limit During Balance

P231C indicates that the powertrain control module (PCM) has detected an air-fuel ratio imbalance on cylinder 9 that is severe enough to reach the adjustment limit during a balance test. The PCM monitors crankshaft speed fluctuations during a fuel-cut balance routine and identifies cylinder 9 as contributing disproportionately to the imbalance, meaning the fuel trim correction for that cylinder has maxed out.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaIgnition system and misfire

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

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