DTC P0421: Notes

DTC P0421 DETECTION CONDITION AND POSSIBLE CAUSES

DTC P0421	Warm up catalyst system efficiency below threshold
DETECTION CONDITION	The PCM compares the number of front HO2S and rear HO2S inversions for a predetermined time. The PCM monitors the rear HO2S inversion counts when the following conditions are met: The PCM detects inversion ratio. If the inversion ratio is below threshold, the PCM determine that catalyst system has deteriorated. The front HO2S inversion counts is as prescribed when the following monitoring conditions are met: The accumulated occurrence time of the following monitoring conditions has exceeded the prescribed time limit: MONITORING CONDITION Engine speed is 1,600-3,000 RPM. Calculated TWC temperature is above 400 °C {752 °F}. Calculated load is 15-48% (at engine speed 2,000 RPM ) Diagnostic support note This is a intermittent monitor (Catalyst). MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM. PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle. DIAGNOSTIC MONITORING TEST RESULTS is available. FREEZE FRAME DATA is available. The DTC is stored in the PCM memory.
POSSIBLE CAUSE	TWC deterioration or malfunction Exhaust gas leakage Loose front HO2S Loose rear HO2S PCM malfunction

DTC P0421

Warm up catalyst system efficiency below threshold

DETECTION CONDITION

The PCM compares the number of front HO2S and rear HO2S inversions for a predetermined time. The PCM monitors the rear HO2S inversion counts when the following conditions are met: The PCM detects inversion ratio. If the inversion ratio is below threshold, the PCM determine that catalyst system has deteriorated.
- The front HO2S inversion counts is as prescribed when the following monitoring conditions are met:
- The accumulated occurrence time of the following monitoring conditions has exceeded the prescribed time limit:

MONITORING CONDITION

Diagnostic support note

This is a intermittent monitor (Catalyst).
MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle.
DIAGNOSTIC MONITORING TEST RESULTS is available.
FREEZE FRAME DATA is available.
The DTC is stored in the PCM memory.

POSSIBLE CAUSE