DTC P0420 LE5

Diagnostic Instructions

DTC Descriptor

DTC P0420: Catalyst System Low Efficiency

Circuit/System Description

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

A 3-way catalytic converter (TWC) controls emissions by converting hydrocarbons (HC) and carbon monoxide (CO) into carbon dioxide (CO2), and oxides of nitrogen (NOx) into nitrogen. The TWC also stores oxygen. When the listed idle conditions follow the listed driving conditions 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 idle conditions. The ECM compares the pre and post catalyst oxygen sensor signals to determine if the oxygen storage capacity of the catalyst is degraded.

Conditions for Running the DTC

Driving Conditions

Idle Conditions

Conditions for Setting the DTC

Action Taken When the DTC Sets

DTC P0420 is a Type B DTC.

Conditions for Clearing the MIL/DTC

DTC P0420 is a Type B DTC.

Reference Information

Electrical Information Reference

DTC Types Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Verify that no other DTCs are set.

⇒	If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Operate the vehicle within the Conditions for Running the DTC while observing the scan tool TWC Mon. OFF Idle Test Conditions Met parameter. The parameter will change to Yes when the OFF Idle Conditions have been met.

⇒	If not the specified value, operate the vehicle within the OFF Idle Conditions.

3. When the parameter has changed to Yes and the conditions are safe, stop and idle the vehicle in gear.
4. Apply the service brake.
5. Monitor the scan tool TWC Monitor Test State parameter. When the parameter indicates Active, the TWC Mon Test is running.
6. Continue to monitor the parameter. When the parameter indicates Inactive, the TWC Mon Test has completed.
7. When the test has completed, the TWC Monitor Test Count parameter will increment by one and the TWC Monitor Test Result parameter will indicate Pass, Fail, or No Decision.

⇒	If no decision has been made, repeat steps 2-6 until the Test Result parameter indicates a Pass or Fail.

Circuit/System Testing

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

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

1. 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

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

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

2. 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.

3. Inspect the exhaust system for the following conditions:

•

Leaks

•	Physical damage

•	Loose or missing hardware

•	Properly torqued HO2S

•	Restrictions

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

4. Inspect the post catalyst HO2S for the following conditions:

•	A grounded wiring harness

•

Damage

⇒	If a condition is found, replace the post catalyst HO2S.

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

Repair Instructions

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

Repair Verification

1. Verify that no other DTCs are set.

⇒	If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Operate the vehicle within the Conditions for Running the DTC while observing the scan tool TWC Mon. OFF Idle Test Conditions Met parameter. The parameter will change to Yes when the OFF Idle Conditions have been met.

⇒	If not the specified value, operate the vehicle within the OFF Idle Conditions.

3. When the parameter has changed to Yes and the conditions are safe, stop and idle the vehicle in gear.
4. Apply the service brake.
5. Monitor the scan tool TWC Monitor Test State parameter. When the parameter indicates Active, the TWC Mon Test is running.
6. Continue to monitor the parameter. When the parameter indicates Inactive, the TWC Mon Test has completed.
7. When the test has completed, the TWC Monitor Test Count parameter will increment by one and the TWC Monitor Test Result parameter will indicate Pass, Fail, or No Decision.

⇒	If no decision has been made, repeat steps 2-6 until the Test Result parameter indicates a Pass or Fail.

DTC P0420 LAT

Diagnostic Instructions

DTC Descriptor

DTC P0420: Catalyst System Low Efficiency Bank 1

Circuit/System Description

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

A 3-way catalytic converter (TWC) controls emissions by converting hydrocarbons (HC) and carbon monoxide (CO) into carbon dioxide (CO2), and oxides of nitrogen (NOx) into nitrogen. The TWC also stores oxygen. 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 deceleration fuel cut-off (DFCO) conditions. The ECM compares the pre and post-catalyst oxygen sensor signals to determine if the oxygen storage capacity of the catalyst is degraded.

Conditions for Running the DTC

1. Driving Conditions

•

DTCs P0010, P0011, P0013, P0014, P0016, P0017, P0030, P0036, P0053, P0054, P0068, P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P013A, P013B, P013E, P013F, P0140, P0141, P0171, P0172, P0220, P0222, P0223, P0300, P0315, P0335, P0336, P0340, P0341, P0365, P0366, P0443, P0496, P0506, P0507, P1133, P1174, P1516, P2101, P2119, P2135, P2176, P2270, P2271, P2A00 are not set.

•	The vehicle has been driven at more than 900 RPM for more than 20 seconds above 43 km/h (27 mph).

•	The vehicle is in Closed Loop.

•	The fuel level is greater than 10 percent.

•	The vehicle has Fuel Trim Learn enabled.

•	The Engine Coolant Temperature (ECT) parameter is between 70-128°C (158-262°F).

•	The Barometric Pressure (BARO) parameter is more than 70 kPa.

•	The Catalytic Converter Calculated Temperature parameter is greater than or equal to 500°C (932°F) for more than 1 minute.

•	The Intake Air Temperature (IAT) parameter is between -20 and +100°C (-4 and +212°F).

•	The battery voltage is more than 11 volts.

2. DFCO Conditions

•	The DFCO period is greater than 1.75 seconds.

•	The heated oxygen sensor (HO2S) 1 is less than 300 mV prior to DFCO exit.

•	The HO2S 2 is less than 300 mV for 2 seconds prior to DFCO exit.

3. DFCO Exit Conditions

•	The throttle position (TP) sensor travel is less than 30 percent.

•	The equivalence ratio is greater than 1.

Conditions for Setting the DTC

Action Taken When the DTC Sets

DTC P0420 is a Type A DTC.

Conditions for Clearing the MIL/DTC

DTC P0420 is a Type A DTC.

Reference Information

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Electrical Information Reference

Diagnostic Trouble Code (DTC) List - Vehicle

Circuit/System Verification

1. Verify that no other DTCs are set.

⇒	If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Clear the DTCs.
3. Operate the vehicle according to the Driving Conditions within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
4. After the Driving Conditions have been met, drive the vehicle at approximately 80 km/h (50 mph) for 60 seconds.
5. Perform a closed throttle deceleration until the vehicle speed is less then 40 km/h (25 mph).
6. Verify that DTC P0420 has passed this ignition cycle.

⇒	If not passed or failed this ignition cycle, the test aborted resulting in an inconclusive test result. The above test may need to be repeated up to 5 more times during this drive cycle.

Circuit/System Testing

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 100 miles on it may set DTC P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

1. Ignition OFF, open the hood to disable the Auto-Stop function.
2. Ignition ON, verify the scan tool Hood Position parameter displays Open.

⇒	If the Hood Position parameter does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

3. 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 minutes and retest the converter.

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 HO2S

•	Restrictions

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

6. Inspect the post catalyst HO2S for the following conditions:

•	A grounded wiring harness

•

Damage

⇒	If a condition is found, replace the post catalyst HO2S.

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

Repair Instructions

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

Repair Verification

1. Clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
3. After the conditions for running the DTC have been met, drive the vehicle at approximately 80 km/h (50 mph) for 60 seconds.
4. Perform a closed throttle deceleration until the vehicle speed is less then 40 km/h (25 mph).
5. Verify that DTC P0420 has passed this ignition cycle.

⇒	If not passed or failed this ignition cycle, the test aborted resulting in an inconclusive test result. The above test may need to be repeated up to 5 more times during this drive cycle.