P0420
DTC P0420 or P0430
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) 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
In order to maintain a reasonably low emission level of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) a 3-way catalytic converter (TWC) is used. The catalyst within the converter promotes a chemical reaction that oxidizes the HC and CO present in the exhaust gas. This reaction converts the gases into harmless water vapor and carbon dioxide. The catalyst also reduces the NOx , converting the NOx into nitrogen. The engine control module (ECM) monitors this process using the post catalyst heated oxygen sensor (HO2S) signal. The post-catalyst HO2S located in the exhaust stream after the TWC, produces an output signal that indicates the oxygen storage capacity of the catalyst. The oxygen storage capacity (OSC) determines the ability of the catalyst to convert the exhaust emissions effectively. If the catalyst is functioning correctly, the post-catalyst HO2S signal will be far less active than the signal produced by the pre-catalyst HO2S.
To determine OSC, the ECM commands a rich air/fuel mixture until all oxygen is removed from the catalyst. The ECM then commands a lean air/fuel mixture and monitors the rear heated oxygen sensors to calculate the oxygen storage capacity. The catalyst is operated in this mode until one of the following conditions occur:
* The oxygen stored in the catalyst exceeds a calibrated threshold, which is determined from the rear HO2S signal.
* The rear HO2S indicates the catalyst to be completely saturated with oxygen, which is determined from the rear HO2S signal.
Conditions for Running the DTC
* Before the ECM can report DTC P0420 or P0430 failed, DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0100, P0101, P0102, P0103, P0121, P0122, P0123, P0131, P0132, P0133, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0155, P0157, P0158, P0160, P0161, P0221, P0222, P0223, P0335, P0336, P0338, P2096, P2097, P2098, P2099, P2195, P2196, P2197, P2198, P2232, P2235, P2237, P2240, P2243, P2247, P2251, P2254, P2270, P2271, P2272, P2273, P2297, P2298, P2626, and P2629 must run and pass.
* DTC P0010, P0011, P0013, P0014, P0020, P0021, P0023, P0024, P0030, P0031, P0032, P0050, P0051, P0052, P0100, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0155, P0157, P0158, P0160, P0161, P0221, P0222, P0223, P0300, P0301-P0306, P0443, P0455, P0458, P0459, P0496, P2088, P2089, P2090, P2091, P2092, P2093, P2094, P2095, P2096, P2097, P2098, P2099, P2100, P2101, P2107, P2119, P2122, P2123, P2127, P2128, P2138, P2176, P2177, P2178, P2179, P2180, P2187, P2188, P2189, P2190, P2232, P2235, P2270, P2271, P2272, or P2273 is not set.
* The engine speed is 1,040-2,280 RPM.
* The engine load is 15-50 percent.
* The air flow into the engine is between 4-15 g/s and steady.
* The engine intake air temperature (IAT) at engine start-up is greater than -10°C (+14°F).
* The engine is operating for greater than 7 minutes.
* The engine is operating in Closed Loop.
* The calculated TWC temperature is between 500-730°C (932-1,346°F) and steady.
* The above conditions exist for approximately 17 minutes.
* After a DTC clear, the ECM will attempt to run this diagnostic up to 4 times a drive cycle for the first 3 drive cycles.
* DTCs P0420 and P0430 run once a drive cycle. The ECM will attempt to run this diagnostic up to 4 times a drive cycle.
Conditions for Setting the DTC
The ECM determines that the efficiency of the catalyst has degraded below a calibrated threshold for greater than 4 seconds.
Action Taken When the DTC Sets
DTCs P0420 and P0430 are Type A DTCs.
Conditions for Clearing the DTC
DTCs P0420 and P0430 are Type A DTCs.
Diagnostic Aids
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
Reference Information
Schematic Reference
Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Testing
1. Observe the DTC information with a scan tool. Verify there are no HO2S, or misfire DTCs set.
• If there are any HO2S or misfire DTCs set, diagnosis the applicable DTC before proceeding with this diagnostic procedure. Refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions) .
2. Inspect and verify the following:
* The catalytic converter is an original part
* The HO2S 2 is secure and the wiring is not damaged, or contacting the exhaust
* The exhaust system for leaks, damage, or missing hardware
• If a condition is found, repair as necessary.
Important: Before replacing the catalytic converter, correct any conditions that may have damaged the converter.
3. If a condition is not located, replace the catalytic converter.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Catalytic Converter Replacement - Left Side (LY7 - Gas, 6 Cylinder, 3.6L, SFI, V6) (Catalytic Converter Replacement - Left Side)
* Catalytic Converter Replacement - Right Side (LY7 - Gas, 6 Cylinder, 3.6L, SFI, V6) (Catalytic Converter Replacement - Right Side)