Note: A new converter with less than 160 km (100 mi) on it may set DTC P0420 00 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 h may correct the condition.

A 3-way catalytic converter controls emissions by converting hydrocarbons and carbon monoxide (CO) into carbon dioxide (CO2), and oxides of nitrogen (NOx) into nitrogen. The TWC also stores oxygen. When the listed driving conditions are met, the Catalyst System Efficiency test will run. The engine control module (ECM) monitors this oxygen storage capacity by comparing the pre- and post-catalyst oxygen sensor signals while adding and subtracting fuel during specific driving conditions. The ECM compares the pre-and post-catalyst oxygen sensor signals to determine if the oxygen storage capacity of the catalyst is degraded.

DTC P0420 is a Type A DTC.

DTC P0420 is a Type A DTC.

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Caution: Refer to Three-Way Catalytic Converter Damage Caution in the Preface section.

Caution: Refer to Heated Oxygen Sensor Resistance Learn Reset Caution in the Preface section.

Note: A new converter with less than 160 km (100 miles) on it may set DTC P0420 00 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 h may correct the condition.

1. If any other DTCs are set perform those diagnostics first.
2. Inspect for the following conditions which may cause a catalytic converter to degrade:

•	An engine misfire

•	High engine oil or high coolant consumption

•	Retarded spark timing

•	A weak or poor spark

•	A lean fuel mixture

•	A rich fuel mixture

•	A damaged oxygen sensor or wiring harness

•	The catalyst test may abort if the vehicle falls outside the conditions for running the DTC.

•	A catalyst may be temporarily degraded if a fuel with high sulfur content has been used. Drive the vehicle at highway speeds for 10 min and retest the converter.

3. Operate the vehicle within the conditions for running the DTC.

⇒	If the DTC fails this key cycle, continue with this procedure.

4. Inspect the catalytic converter for the following conditions:

•

Dents

•	A severe discoloration caused by excessive temperatures

•	Road damage

•	An internal rattle caused by damaged catalyst substrate

•	Restrictions

⇒	If a condition is found, replace the catalytic converter.

5. Inspect the exhaust system for the following conditions:

•

Leaks

•	Physical damage

•	Loose or missing hardware

•	Properly torqued B52A Heated Oxygen Sensor (HO2S)

•	Restrictions

⇒	If a condition is found, repair the exhaust system.

6. Inspect the B52B Heated Oxygen Sensor (HO2S) for the following conditions:

•	A grounded wiring harness

•

Damage

⇒	If a condition is found, replace the B52B Heated Oxygen Sensor (HO2S).

⇒	If no physical condition is detected, replace the catalytic converter.

Note: A new converter with less than 160 km (100 mi) on it may set DTC P0420 00 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 h may correct the condition.

1. Clear the DTCs.
2. Operate the vehicle within the Conditions for Running and Setting for at least 10 min.
3. Stop the vehicle.
4. Engine OFF, allow the ECM to power down.
5. Operate the vehicle within the Conditions for Running and Setting for at least 10 min. DTC P0420 00 should run and pass.