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MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS TSB Revision MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE> 13A-598 13A DTC P0421: Warm Up Catalyst Efficiency Below Threshold (cylinder 1, 4) . TECHNICAL DESCRIPTION • The signal from the rear heated oxygen sensor differs from the front heated oxygen sensor. That • The PCM compares the output of the front and rear heated oxygen sensor signals. . DESCRIPTIONS OF MONITOR METHODS Front and rear heated oxygen sensor rich/lean switching frequencies are nearly equal. . MONITOR EXECUTION Continuous . MONITOR EXECUTION CONDITIONS Other Monitor (There is no temporary DTC stored in memory for the item monitored below) • Heated oxygen sensor (front) monitor • Heated oxygen sensor (rear) monitor • Heated oxygen sensor heater (front) monitor • Heated oxygen sensor heater (rear) monitor • Misfire monitor • Fuel system monitor • Air/fuel ratio feedback monitor Sensor (The sensor below is determined to be normal) • Mass airflow sensor • Engine coolant temperature sensor • Intake air temperature sensor • Barometric pressure sensor • Throttle position sensor • Accelerator pedal position sensor . DTC SET CONDITIONS . START MONITORING CONDITIONS MALFUNCTION GOOD END NO NO YES YES Rf > R0 CALCULATE AVERAGE FREQUENCY RATIO (Rf = Fr/Ff) OF SPECIFIED TIMES R0: AVERAGE THRESHOLD VALUE. AK302038 <<PREVIOUS |