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
Important: A new converter with less than 100 miles 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 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
1. Driving Conditions
* DTCs 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 (manual transmission only), P0502, P0506, P0507, P0601, P0602, P0606, P0641, P0722, P0723, P1133, P1134, P1516, P1621, P2135, P2138, P2176 are not set.
* The engine has been running for more than 2 minutes.
* The vehicle has been driven at more than 1,000 RPM for more than 10 seconds.
* The vehicle is in Closed Loop.
* The vehicle has Fuel Trim Learn enabled.
* The engine coolant temperature (ECT) is between 45-128°C (113-262°F).
* The barometric pressure (BARO) parameter is more than 70 kPa.
* The catalytic converter calculated temperature is greater than or equal to 375°C (707°F).
* The intake air temperature (IAT) parameter is between -20 and +85°C (-4 and +185°F).
* The battery voltage is more than 11 volts.
2. Idle Conditions
* The vehicle speed is less than 3.2 km/h (2 mph).
* For automatic transmissions, the transmission is in Reverse, Drive, or Low.
* The throttle position (TP) is 2 percent or less.
* The short term fuel trim (FT) is between -10 and +10 percent.
* This diagnostic attempts one test during each valid idle period when the above conditions have been met. This diagnostic attempts up to 6 tests during each drive cycle.
Conditions for Setting the DTC
* The ECM has determined the catalyst efficiency has degraded below a calibrated threshold.
* This diagnostic may conclude in one test attempt. However, this diagnostic may require as many as 18 test attempts, which would require at least 3 drive cycles. Each test attempt may conclude within approximately 1 minute.
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
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)
* Heated Oxygen Sensor 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 Verification
Notice: Refer to Three-Way Catalytic Converter Damage Notice (Service Precautions) .
Notice: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice (Heated Oxygen Sensor Resistance Learn Reset Notice) .
Important: A new converter with less than 100 miles 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 hour may correct the condition.
1. If any other DTCs are set perform those diagnostics first.
2. 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.
3. Operate the vehicle within the Conditions for Running the DTC.
• If the DTC fails this key cycle, continue with this procedure.
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.
• If no physical condition is detected, replace the catalytic converter.
Repair Instructions
Important: A new converter with less than 100 miles 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 hour may correct the condition.
* Exhaust Manifold Replacement - Left Side (LH8) (Exhaust Manifold Replacement - Left Side)
* Exhaust Manifold Replacement - Right Side (LH8) (Exhaust Manifold Replacement - Right Side)
* Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 (Heated Oxygen Sensor Replacement - Bank 1 Sensor 1)
* Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 (Heated Oxygen Sensor Replacement - Bank 2 Sensor 2)
* Exhaust Leakage (Exhaust Leakage)
* Restricted Exhaust (Restricted Exhaust)
Repair Verification
1. Clear the DTCs.
2. Allow the engine coolant temperature to reach 70°C (156°F).
* Place the gear selector in Park, Neutral for manual.
* Set the parking brake.
3. Press and hold the service brake.
4. Run the engine for 6 minutes at 2500 RPM.
5. Allow engine speed to return to idle speed, then place gear selector into Drive, or apply clutch pedal for manual.
6. After 2 minutes verify that DTC P0420 or P0430 have passed or failed 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. The first test should be run after the initial warm up period of 6 minutes. Between subsequent tests maintain 2,500 RPM for 2 minutes.
7. If 6 tests have been attempted and the DTC has not run or passed during this key cycle, turn the key to OFF for 30 seconds, then run the procedure a second time.