Note: A new converter with less than 160 km/h (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.

A 3-way catalytic converter (TWC) controls emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction, which oxidizes the HC and the CO that are present in the exhaust gas. This process converts the HC and the CO into water vapor and carbon dioxide (CO2), and reduces the NOx, converting the NOx into nitrogen. The catalytic converter also stores oxygen. The engine control module (ECM) monitors this process by using a heated oxygen sensor (HO2S) that is in the exhaust stream after the TWC. The HO2S 2 produces an output signal that the ECM uses to calculate the oxygen storage capacity of the catalyst. This indicates the ability of the catalyst to convert the exhaust emissions efficiently. The ECM monitors the efficiency of the catalyst by allowing the catalyst to heat, then wait for a stabilization period while the engine is idling. The ECM then adds and removes fuel while monitoring the HO2S 2. When the catalyst is functioning properly, the HO2S 2 response to the extra fuel is slow compared to the response of the HO2S 1, which is located before the TWC. When the HO2S 2 response is near that of the HO2S 1, the oxygen storage capability and efficiency of the catalyst may be degraded below an acceptable threshold.

The ECM determines that the efficiency of the catalyst has degraded below a calibrated threshold.

DTC P0420 is a Type A DTC.

DTC P0420 is a Type A DTC.

Inspect for the following conditions, which may cause a catalytic converter to degrade:

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Engine idling, observe the DTC information with a scan tool. Verify there are no HO2S or misfire DTCs set.

⇒	⇒ If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnosis the applicable DTC, before proceeding with this diagnostic procedure.

2. Verify the following conditions do not exist with the catalytic converter:

•

Dents

•	A severe discoloration caused by excessive temperatures

•	Road damage

•	An internal rattle caused by damaged catalyst subset

•	Restrictions

⇒	If a condition is found, replace the catalytic converter

3. Verify the following conditions do not exist with the exhaust system:

•

Leaks

•	Physical damage

•	Loose or missing hardware

•	Properly torqued B52A Heated Oxygen Sensor (HO2S) or B52B Heated Oxygen Sensor (HO2S)

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

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

4. Verify the following conditions do not exist with the B52B Heated Oxygen Sensor (HO2S)

•	A grounded B52B Heated Oxygen Sensor (HO2S) wiring harness

•

Damage

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

5. If no physical condition is detected and the B52B Heated Oxygen Sensor (HO2S) is as active as the B52A Heated Oxygen Sensor (HO2S) after operating the engine at 1500 RPM for 1 min and then returning to a stabilized idle, then replace the catalytic converter.

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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.