P0420
DTC P0420
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P0420
- Catalyst System Low Efficiency
Circuit/System Description
A 3-way catalyst controls emissions of hydrocarbons, carbon monoxide (CO) and nitrogen oxide (NOx). The catalyst within the converter promotes a chemical reaction, which oxidizes the hydrocarbons and the CO that are present in the exhaust gas. This process converts the hydrocarbons and the CO into water vapor and carbon dioxide (CO2), and reduces the NOx, converting the NOx into nitrogen. The catalyst also stores oxygen. The engine control module (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, 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.
Conditions for Running the DTC
* DTC P0030, P0031, P0032, P0036, P0037, P0038, P0053, P0054, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0135, P0137, P0138, P013A, P013B, P013E, P013F, P0141, P015A, P015B, P0171, P0172, P0201, P0202, P0203, P0204, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0300, P0301, P0302, P0303, P0304, P1248, P1249, P124A, P124B, P16F3, P2101, P2135, P2147, P2148, P2150, P2151, P2153, P2154, P2156, P2157, P2270, or P2271 is not set.
* The engine speed is between 1,250-2,300 RPM to enable the catalyst diagnostic. Once the engine speed is in range, the engine speed must be between 1,100-2,450 RPM to keep the test enabled.
* The accelerator pedal position is at most 4 %.
* Ethanol estimation is not active.
* The evaporative emission (EVAP) purge is not active.
* The post HO2S heater is ON for greater than 180 s.
* The mass air flow (MAF) is between 3-12 g/s.
* The system voltage is between 10-32 V.
* The vehicle speed is between 55-121 km/h (34-75 MPH) to enable the catalyst diagnostic. To keep the test enabled the vehicle speed is between 52-132 km/h (32-82 MPH).
* The catalyst calculated temperature is between 600-900°C (1,112-1,652°F).
* The engine is operating in closed loop.
* The engine is operating in Decel Fuel Cut Off (DFCO).
This diagnostic attempts one test during each valid OFF-idle period once the above conditions have been met. This diagnostic attempts up to 3 tests during each drive cycle.
Conditions for Setting the DTC
The ECM has detected that the catalyst efficiency has degraded below a calibrated threshold.
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
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
* Heated Oxygen Sensor Wiring Repairs Heated Oxygen Sensor Wiring Repairs
DTC Types Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
1. Ignition ON.
2. Verify there are no other DTCs set.
• If a DTC is set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
• If a DTC is not set
3. Operate the vehicle within the Conditions for Running the DTC.
4. Verify the scan tool Catalyst Monitor Not At Idle Test Conditions Met parameter changes to Yes.
• If Yes is not displayed
Refer to step 3.
• If Yes is displayed
5. Monitor the scan tool Catalyst Monitor Test State parameter. When the parameter indicates Active, the Catalyst Monitor Test is running.
Note: When the test has completed, the Catalyst Monitor Test Counter parameter will increment by one and the Catalyst Monitor Test Result parameter will indicate Passed, Failed or No Result.
6. Continue to monitor the parameter. When the parameter indicates Inactive, the Catalyst Monitor Test has completed.
• If the Catalyst Monitor Test Result parameter indicates No Result
Repeat steps 3-6 until the Test Result parameter indicates Passed or Failed
• If the Catalyst Monitor Test Result parameter indicates Failed
Refer to Circuit /System Testing
• If the Catalyst Monitor Test Result parameter indicates Pass
7. All OK.
Circuit/System Testing
1. Verify the conditions listed below do not exist with the catalytic converter:
* Dents
* Severe discoloration caused by excessive temperatures
* Road damage
* Internal rattles caused by damaged catalyst substrate
* Restrictions
• If a condition is found
Replace the catalytic converter.
• If no condition is found
2. Verify the conditions listed below do not exist with the exhaust system:
* Leaks
* Physical damage
* Loose or missing hardware
• If a condition is found
Repair or replace the component as necessary.
• If no condition is found
3. Verify the conditions listed below do not exist with the B52B heated oxygen sensor 2:
* Incorrect torque
* Damage
• If a condition is found
Replace the B52B heated oxygen sensor 2 or repair the condition as necessary.
• If no condition is found
4. Test or replace the catalytic converter.
Repair Instructions
* Catalytic Converter Replacement (LHU) Catalytic Converter ReplacementCatalytic Converter Replacement (LUK) Catalytic Converter Replacement
* Exhaust Leakage Exhaust Leakage
* Heated Oxygen Sensor Replacement - Sensor 2 Heated Oxygen Sensor Replacement - Sensor 2
* Restricted Exhaust Restricted Exhaust
Repair Verification
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. Turn OFF the ignition for 60 s
5. Operate the vehicle within the Conditions for Running the DTC.
6. Verify the scan tool Catalyst Monitor Not At Idle Test Conditions Met parameter changes to Yes.
• If Yes is not displayed
Refer to step 5.
• If Yes is displayed
7. Monitor the scan tool Catalyst Monitor Test State parameter. When the parameter indicates Active, the Catalyst Monitor Test is running.
Note: When the test has completed, the Catalyst Monitor Test Counter parameter will increment by one and the Catalyst Monitor Test Result parameter will indicate Passed, Failed or No Result.
8. Continue to monitor the parameter. When the parameter indicates Inactive, the Catalyst Monitor Test has completed.
• If the Catalyst Monitor Test Result parameter indicates No Result
Repeat steps 5-8 until the Test Result parameter indicates Passed or Failed
• If the Catalyst Monitor Test Result parameter indicates Failed
Refer to Circuit /System Testing
• If the Catalyst Monitor Test Result parameter indicates Pass
9. All OK.