P0420
DTC P0420
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)provide an overview of each diagnostic category.
DTC Descriptor
DTC P0420
- Catalyst System Low Efficiency
Circuit/System Description
A 3-way catalytic (TWC) converter controls emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). 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.
Important: A new converter with less than 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.
Conditions for Running the DTC
1. Driving Conditions
* DTCs P0030, P0036, P0053, P0054, P0059, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0151-P0155, P0171, P0172, P0174, P0175, P0201-P0208, P0220, P0222, P0223, P0315, P0300, P0301-P0308, P0335, P0336, P0340, P0341, P0351-P0358, P0401, P0403, P0404, P0405, P0406, P0411, P0412, P0418, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P0506, P0507, P060D, P1101, P1133, P1153, P1174, P1175, P1258, P1400, P1404, P1516, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, P2176, P2430, P2431, P2432, P2433, P2440, P2444, P2A00, P2A01, P2A03, or U0107 are not set.
* The engine has been running for greater than 6 minutes.
* The vehicle is in Closed Loop.
* The vehicle has Fuel Trim enabled.
* The engine coolant temperature (ECT) is between 70-125°C (158-257°F).
* The barometric pressure (BARO) is greater than 70 kPa.
* The intake air temperature (IAT) is greater than -20°C (-4°F).
* The throttle position (TP) is less than 2 percent.
* The calculated TWC temperature (Calc. TWC Temp.) is between 385-640°C (725-1,184°F).
* The battery voltage is greater than 10.7 volts.
2. Idle Conditions
* The vehicle speed is less than 3.2 km/h (2 mph).
* The engine speed has been greater than 1,200 RPM for 25 seconds.
* The automatic transmission is in Reverse, Drive, or Low.
* The TP is less than 2 percent.
* The short term fuel trim (FT) is between -10 and +10 percent.
* The engine speed is less than 1,000 RPM.
* The engine idle is stable.
* This diagnostic attempts one test during each valid idle period when the above conditions have been met. These diagnostic attempts up to 6 tests during each drive cycle.
Conditions for Setting the DTC
* The ECM has determined that 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
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 (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
Programming and Relearning (Programming and Relearning)for scan tool information
Circuit/System Verification
Notice: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice (Heated Oxygen Sensor Resistance Learn Reset Notice) .
Notice: Refer to Three-Way Catalytic Converter Damage Notice (Service Precautions) .
1. Verify that no other DTCs are set.
• If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions) .
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
* 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.
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.
7. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Repair Instructions
* Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 (Service and Repair)
* Exhaust System Replacement (Service and Repair)
* Exhaust System Insulator, Hanger, Bracket Replacement (Service and Repair)
* Restricted Exhaust (Restricted Exhaust)
Repair Verification
1. Clear all 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 2,500 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 has 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.