DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (EXCEPT CALIF. EMISSIONS) Circuit Description ECM compares waveform of heated oxygen sensor located in front of catalytic converter with waveform of heated oxygen sensor located behind converter to determine if converter performance has deteriorated. If both waveforms change at similar rate, catalyst performance has deteriorated. DTC is set when both oxygen sensors have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are: l Defective catalytic converter. L Heated oxygen sensor circuit is open or shorted. L Defective heated oxygen sensor. Diagnostic Aids Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected. Diagnosis & Repair 1. If any other DTCs are displayed, diagnose and repair those DTCs first. If only DTC P0420 is displayed, go to next step. 2. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, go to next step. 3. Check heated oxygen sensor No. 1. See DTC P0130: HEATED OXYGEN SENSOR NO. 1 CIRCUIT (EXCEPT CALIF. EMISSIONS). If problem exists, repair as necessary. If problem does not exist, go to next step. 4. Check heated oxygen sensor No. 2. See DTC P0136: HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 2) test. If problem exists, repair as necessary. If problem does not exist, replace catalytic converter. DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (CALIF. EMISSIONS) NOTE: Heated oxygen sensor No. 1 refers to oxygen sensor closest to engine block. Heated oxygen sensor No. 2 refers to oxygen sensor farthest from engine block. NOTE: For component location, see appropriate illustration in THEORY & OPERATION article. NOTE: For component location, see appropriate illustration in THEORY &Circuit Description ECM monitors heated oxygen sensor No. 2 (located behind converter) to determine if converter performance has deteriorated. If converter is functioning properly, heated oxygen sensor waveform switches back and forth between rich and lean more slowly. DTC is set when A/F sensor and heated oxygen sensor No. 2 have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are: l Defective catalytic converter. L Heated oxygen sensor No. 2 circuit is open or shorted. L Defective heated oxygen sensor No. 2. L Defective Air/Fuel (A/F) sensor. L A/F sensor circuit is open or shorted. Diagnostic Aids Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected. Diagnosis & Repair 1. If any other DTCs are displayed, diagnose and repair those DTCs first. If only DTC P0420 is displayed, go to next step. 2. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, go to next step. 3. Check A/F sensor. See DTC P1130: AIR/FUEL SENSOR CIRCUIT RANGE/PERFORMANCE (CALIF. EMISSIONS). If problem exists, repair as necessary. If problem does not exist, go to next step. 4. Check heated oxygen sensor No. 2. See DTC P0136: HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 2) test. If problem exists, repair as necessary. If problem does not exist, replace catalytic converter. OPERATION article
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Thursday, February 4th, 2010 AT 3:37 AM
