P0420
DTC P0420 or P0430
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 Descriptors
DTC P0420
- Catalyst System Low Efficiency Bank 1
DTC P0430
- Catalyst System Low Efficiency Bank 2
Circuit/System Description
A 3-way catalytic converter controls emissions of hydrocarbons, CO and 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 CO2, and reduces the NOx, by converting the NOx into nitrogen. The catalytic converter also stores oxygen. The ECM monitors this process by using a heated oxygen sensor (HO2S) that is in the exhaust stream after the 3-way catalytic converter. 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 3-way catalytic converter. 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.
Conditions for Running the DTC
* DTC P0030, P0031, P0036, P0037, P0038, P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0220, P0300, P0315, P0326, P0327, P0336, P0340, P0341, P0442, P0446, P0452, P0453, P0455, P0496, P0500, P0502, P0506, P0507, P0601, P0602, P0606, P0641, P0722, P0723, P1133, P1134, P1516, P1621, P2135, P2138, or P2176 is not set.
* Before the ECM performs the idle test, the vehicle must be driven under the following conditions:
- The engine speed is greater than 1,300 RPM.
- The engine run time is greater than 100 s.
- Both conditions exist for greater than 16 s.
* The vehicle speed is less than 1.6 km/h (1 mph).
* The throttle position is less than 2 %.
* The Mass Air Flow (MAF) is between 2-21 g/s.
* The engine is operating in Closed Loop.
* The fuel trim learn is enabled.
* The Engine Coolant Temperature (ECT) is between 45-129°C (113-264°F).
* The Barometric Pressure (BARO) is greater than 70 kPa.
* The Catalytic Converter Calculated Temperature parameter is between 600-900°C (1,112-1,652°F) for greater than 6 min.
* The Intake Air Temperature (IAT) is between -20 and +250°C (-4 and +482°F).
* The battery voltage is greater than 11 V.
* The transmission is in Drive Range-Automatic transmissions only.
* The short term fuel trim is between -10 and +10 %.
* The engine is idling for less than 50 s.
* This diagnostic attempts one test during each valid idle period when the above conditions have been met. This diagnostic attempts up to 8 tests during each drive cycle.
Conditions for Setting the DTC
The ECM has determined the catalyst efficiency has degraded below a calibrated threshold.
Action Taken When the DTC Sets
DTCs P0420 and P0430 are Type A DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0420 and P0430 are Type A DTCs.
Reference Information
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Electrical Information Reference
Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle
Circuit/System Verification
1. Verify that no other DTCs are set.
• If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.
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 Monitor Test is running.
6. Continue to monitor the parameter. When the parameter indicates Inactive, the TWC Monitor Test has completed.
7. When the test has completed, the TWC Mon. Test Count Bank 1 and Bank 2 parameter will increment by one and the TWC Mon.Test Result Bank 1 and Bank 2 parameter will indicate Passed, Failed or No Result.
• If No Result is indicated, repeat steps 2-6 until the Test Result parameters indicate Passed or Failed.
Circuit/System Testing
1. Verify the following conditions do not exist with the catalytic converter:
* Dents
* A severe discoloration caused by excessive temperatures
* An internal rattle caused by damaged catalyst substrate
* Restrictions-Refer to Restricted Exhaust Restricted Exhaust.
• If a condition is found, replace the catalytic converter.
2. Verify the following conditions do not exist with the exhaust system:
* Leaks-Refer to Exhaust Leakage Exhaust Leakage.
* 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 HO2S 2:
* HO2S not at the correct torque
* Damage
• If a condition is found, replace the HO2S 2 as necessary.
4. If all physical conditions test normal, test or replace the catalytic converter.
Repair Instructions
Note: A new converter with less than 161 km (100 mi) on it may set DTC P0420 or P0430 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 h may correct the condition.
* Catalytic Converter Replacement - Left Side
* Catalytic Converter Replacement - Right Side
* Heated Oxygen Sensor Replacement - Bank 1 Sensor 2
* Heated Oxygen Sensor Replacement - Bank 2 Sensor 2
* Perform the HO2S Heater Learn procedure with a scan tool after replacing an HO2S.
* Exhaust Leakage Exhaust Leakage
* 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 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.
6. When the parameter has changed to Yes and the conditions are safe, stop and idle the vehicle in gear.
7. Apply the service brake.
8. Monitor the scan tool TWC Test State parameter. When the parameter indicates Active, the TWC Monitor Test is running.
9. Continue to monitor the parameter. When the parameter indicates Inactive, the TWC Monitor Test has completed.
10. When the test has completed, the TWC Mon. Test Count Bank 1 and Bank 2 parameter will increment by one and the TWC Mon.Test Result Bank 1 and Bank 2 parameter will indicate Passed, Failed or No Result.
• If No Result is indicated, repeat steps 5-9 until the Test Result parameters indicate Passed or Failed.
11. 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 Diagnostic Trouble Code (DTC) List - Vehicle