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
Note: A new converter with less than 100 miles on it may set DTC P0420 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 of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction, which oxidizes the HC and the CO that are present in the exhaust gas. This process converts the HC and the CO into water vapor and carbon dioxide (CO2), and reduces the NOx, converting the NOx into nitrogen. The catalytic converter also stores oxygen. The engine control module (ECM) monitors this process by using a heated oxygen sensor (HO2S) that is in the exhaust stream after the TWC. 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 TWC. 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
* 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, or P2A03 are not set.
* Before the ECM performs the idle test, the vehicle must be driven under the following conditions:
- The engine speed is greater than 1,000 RPM
- The engine run time is greater than 120 seconds
- Both conditions exist for greater than 16 seconds
* The vehicle speed is less than 2 km/h (1 mph)
* The throttle position (TP) is less than 2 percent
* The mass air flow (MAF) is greater than 12 g/s for greater than 30 seconds
* The engine is operating in Closed Loop
* The fuel trim learn is enabled
* The Engine Coolant Temperature (ECT) is between 40-130°C (104-266°F)
* The Barometric Pressure (BARO) is greater than 70 kPa
* The Catalytic Converter Calculated Temperature parameter is between 400-640°C (752-1,184°F)
* The Intake Air Temperature (IAT) is greater than -20°C (-4°F)
* The battery voltage is greater than 11 volts
* The transmission is in gear-Automatic transmissions only
* The short term fuel trim (FT) is between -10 and +10 percent
* This diagnostic attempts one test during each valid idle period once 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.
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
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 Testing
Caution: Refer to Heated Oxygen Sensor Resistance Learn Reset Caution (Heated Oxygen Sensor Resistance Learn Reset Caution).
Note: A new converter with less than 100 miles on it may set DTC P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.
1. Engine idling, observe the DTC information with a scan tool. Verify there are no HO2S or misfire DTCs set.
• If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle) to diagnosis the applicable DTC, before proceeding with this diagnostic procedure.
2. 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
• If a condition is found, replace the catalytic converter.
3. Verify the following conditions do not exist with the exhaust system:
* Leaks
* Physical damage
* Loose or missing hardware
* Improperly torqued HO2S
• If a condition is found, repair the exhaust system.
4. Verify the following conditions do not exist with the HO2S 2:
* A grounded wiring harness
* Damage
• If a condition is found, replace the HO2S 2.
5. If no physical condition is detected and the HO2S 2 is as active as the HO2S 1 after operating the engine at 1,500 RPM for 1 minute and then returning to a stabilized idle, then replace the catalytic converter.
Repair Instructions
Note: A new converter with less than 100 miles on it may set DTC P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.
* Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 (Service and Repair)
* Restricted Exhaust (Restricted Exhaust)
* Exhaust Leakage (Exhaust Leakage)
* Catalytic Converter Replacement (Service and Repair)