Possible Causes

GOOD TRIP EQUAL TO ZERO

VISUALLY INSPECT CATALYTIC CONVERTER

EXHAUST LEAK

ENGINE MECHANICAL CONDITION

AGING O2 SENSOR

CATALYTIC CONVERTER

DIAGNOSTIC PROCEDURE - P0420-CATALYTIC 1/1 EFFICIENCY

TEST	ACTION
1	NOTE: A new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set. Review the repair history of the vehicle before continuing. NOTE: If an O2 Sensor or Fuel System Lean DTC(s) is set along with the Catalytic Converter Efficiency DTC, diagnose the O2 Sensor DTC(s) before continuing. NOTE: Check for contaminates that may have damaged the O2 Sensor and Catalytic Converter: contaminated fuel, unapproved silicone, oil and coolant, repair necessary. Ignition on, engine not running.With the DRBIII®, read DTCs and record the related Freeze Frame data.Is the Good Trip Counter displayed and equal to zero? Yes --> Go To 2 No --> Refer to the INTERMITTENT CONDITION symptom in the Driveability category. Perform POWERTRAIN VERIFICATION TEST VER - 5 - NGC .
2	Inspect the Catalytic Converter for the following damage. Damaged Catalytic Converter, dent and holes. Severe discoloration caused by overheating the Catalytic Converter. Catalytic Converter broke internally. Leaking Catalytic Converter. Were any problems found? Yes --> Replace the Catalytic Converter. Repair the condition that may have caused the failure. Perform POWERTRAIN VERIFICATION TEST VER - 5 - NGC . No --> Go To 3
3	Start the engine. Inspect the exhaust for leaks between the engine and the O2 Sensor. Inspect the exhaust for leaks between the engine and the appropriate rear O2 Sensor. Are there any exhaust leaks? Yes --> Repair or replace the leaking exhaust parts as necessary. Perform POWERTRAIN VERIFICATION TEST VER - 5 - NGC . No --> Go To 4
4	Check the exhaust for excessive smoke caused by an internal problem in the engine. Is a engine mechanical condition present? Yes --> Repair the engine mechanical condition as necessary. Perform POWERTRAIN VERIFICATION TEST VER - 5 - NGC . No --> Go To 5
5	A new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set. Review the vehicles repair history. Has the rear O2 Sensor been replaced without replacing the front O2 Sensor? Yes --> Replace the Front O2 Sensor as necessary. Perform POWERTRAIN VERIFICATION TEST VER - 5 - NGC . No --> Go To 6
6	If there are no possible causes remaining, view repair. Repair: Replace the Catalytic Converter. Perform POWERTRAIN VERIFICATION TEST VER - 5 - NGC .