Volt

DTC P0420

A 3-way catalyst controls emissions of hydrocarbons, CO and NOX. The catalyst within the converter promotes a chemical reaction, which oxidises the hydrocarbon(s) and the CO that are present in the exhaust gas. This process converts the hydrocarbon(s) and the CO into water vapor and CO2, and reduces the NOX, converting the NOX into nitrogen. The catalyst also stores oxygen. The ECM monitors this process by using heated oxygen sensors (HO2S) that are in the exhaust stream before and after the 3- way catalyst. The HO2S 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 monitoring the HO2S during an off-idle, ECM commanded Decel Fuel Cut Off (DFCO) event. When the catalyst is functioning properly, the post catalyst HO2S response to the fuel conditions during the DFCO event is slow compared to the response of the pre catalyst HO2S. When the post HO2S response is near that of the pre HO2S, the oxygen storage capability and efficiency of the catalyst may be degraded below an acceptable threshold.

This diagnostic attempts one test during each valid OFF-idle period once the above conditions have been met. This diagnostic attempts up to 6 tests during each drive cycle.

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 catalyst to degrade:

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Hybrid Modes of Operation Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Vehicle in Service Mode, observe the DTC information with a scan tool. Verify there are no other DTCs set.

⇒	If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

2. Engine running, operate the vehicle within the Conditions for Running the DTC. Observe the scan tool Catalyst Monitor Not At Idle Test Conditions Met parameter. The parameter will change to Yes when the Conditions have been met.

⇒	If not the specified value, operate the vehicle within the Conditions for Running the DTC.

3. Monitor the scan tool Catalyst Monitor Test State parameter. When the parameter indicates Active, the Catalyst Monitor Test is running.
4. Continue to monitor the parameter. When the parameter indicates Inactive, the Catalyst Monitor Test has completed.
5. When the test has completed, the Catalyst Monitor Test Counter parameter will increment by one and the Catalyst Monitor Test Result parameter will indicate Pass, Fail, or No Decision.

⇒	If no decision has been made, repeat steps 2-4 until the Test Result parameter indicates Pass or Fail.

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

•

Dents

•	A severe discolouration caused by excessive temperatures

•	Road damage

•	An internal rattle caused by damaged catalyst substrate

•	Restrictions

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

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

•

Leaks

•	Physical damage

•	Loose or missing hardware

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

3. Verify the following conditions do not exist with the B52B Heated Oxygen Sensor 2.

•	The HO2S is not at the correct torque

•

Damage

⇒	If a condition is found, repair or replace the B52B Heated Oxygen Sensor 2 as necessary.

4. If all physical conditions test normal, test or replace the catalytic converter.

1. Install any components that have been removed or replaced during diagnosis.
2. Perform any adjustments, programming or setup procedures that are required when a component is removed or replaced.
3. Clear the DTCs with a scan tool.
4. Vehicle OFF for 60 s.
5. Engine running, operate the vehicle within the Conditions for Running the DTC. Observe the scan tool Catalyst Monitor Not At Idle Test Conditions Met parameter. The parameter will change to Yes when the Conditions have been met.

⇒	If not the specified value, operate the vehicle within the Conditions for Running the DTC.

6. Monitor the scan tool Catalyst Monitor Test State parameter. When the parameter indicates Active, the Catalyst Monitor Test is running.
7. Continue to monitor the parameter. When the parameter indicates Inactive, the Catalyst Monitor Test has completed
8. When the test has completed, the Catalyst Monitor Test Counter parameter will increment by one and the Catalyst Monitor Test Result parameter will indicate Pass, Fail, or No Decision.

⇒	If no decision has been made, repeat steps 5-7 until the Test Result parameter indicates Pass or Fail.

9. If the repair was related to a DTC, duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to the Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.