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
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
Without Hybrid
* DTCs P0030, P0036, P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0220, P0300, P0315, P0326, P0327, P0336, P0340, P0341, P0442, P0446, P0452, P0453, P0455, P0496, P0502, P0506, P0507, P0601, P0602, P1133, P1516, P1621, P2135, P2138, P2176 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 10 minutes
- Both conditions exist for greater than 1 minute
* The throttle is in the rest position.
* The intake air temperature (IAT) is between -20 to +85°C (-4 to +185°F).
* The ignition voltage is greater than 11 volts.
* The engine coolant temperature (ECT) is between 70-125°C (156-257°F).
* The barometric pressure (BARO) is greater than 70 kPa.
* The vehicle speed is less than 3 km/h (2 mph).
* The short term fuel trim is learned.
* The short term fuel trim (FT) is between -10 and +10 percent.
* The engine is operating in Closed Loop.
* The transmission is not in P/N (automatic transmission only).
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
With Hybrid
1. Driving Conditions
* DTCs P0010, P0011, P0013, P0014, P0016, P0017, P0030, P0036, P0053, P0054, P0068, P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P013A, P013B, P013E, P013F, P0140, P0141, P0171, P0172, P0220, P0222, P0223, P0300, P0315, P0335, P0336, P0340, P0341, P0365, P0366, P0443, P0496, P0506, P0507, P1133, P1174, P1516, P2101, P2119, P2135, P2176, P2270, P2271, or P2A00 are not set.
* The vehicle has been driven at greater than 900 RPM for longer than 20 seconds above 43 km/h (27 mph).
* The vehicle is operating in Closed Loop.
* The fuel level is greater than 10 percent.
* The Fuel Trim Learn is enabled.
* The Engine Coolant Temperature (ECT) is between 70-128°C (158-262°F).
* The Barometric Pressure (BARO) is greater than 70 kPa.
* The Catalytic Converter Calculated Temperature is greater than or equal to 500°C (932°F) for longer than 1 minute.
* The Intake Air Temperature (IAT) is between -20 and +100°C (-4 and +212°F).
* The battery voltage is greater than 11 volts.
2. DFCO Conditions
* The DFCO period is greater than 1.75 seconds.
* The heated oxygen sensor (HO2S) 1 is less than 300 mV prior to DFCO exit.
3. DFCO Exit Conditions
* The throttle position (TP) sensor travel is less than 30 percent.
* The equivalence ratio is greater than 1.
This diagnostic attempts one test during each valid idle period once the above conditions have been met. This diagnostic attempts up to 8 tests during each drive cycle.
Conditions for Setting the DTC
The ECM determines that the efficiency of the catalyst has degraded below a calibrated threshold.
Action Taken When the DTC Sets
DTC P0420 is a Type A DTC.
Conditions for Clearing the DTC
DTC P0420 is a Type A DTC.
Diagnostic Aids
Note: A new converter with less than 161 kilometers (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.
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
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Testing
1. Engine idling, observe the DTC information with a scan tool. Verify there are no HO2S or misfire DTCs set.
• If any of the 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
* Road damage
* 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
* Properly 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
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Exhaust Leakage (Exhaust Leakage)
* Restricted Exhaust (Restricted Exhaust)
* Heated Oxygen Sensor Replacement - Sensor 2 (Heated Oxygen Sensor Replacement - Sensor 2)
* Catalytic Converter Replacement ([1][2]Catalytic Converter Replacement)