Powertrain Management
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 160 km (100 mi) on it may set DTC P0420 due to outgassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 h may correct the condition.
A 3-way catalyst controls emissions of hydrocarbons, carbon monoxide (CO), and oxides of nitrogen (NOX). The catalyst within the converter promotes a chemical reaction, which oxidizes the hydrocarbon(s) and the CO that are present in the exhaust gas. This process converts the hydrocarbon(s) and the CO into water vapor and carbon dioxide (CO2), and reduces the NOX, converting the NOX into nitrogen. The catalyst 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 three way catalyst. 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 three way catalyst. 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 P000A, P000B, P0010, P0013, P0016, P0017, P0030, P0031, P0032, P0036, P0038, P0117, P0118, P0119, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0139, P0140, P0141, P0171, P0201, P0202, P0203, P0204, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0301, P0302, P0303, P0304, P0335, P0336, P0340, P0365, P0366, P0443, P0446, P0458, P0459, P0496, P0562, P0563, P0642, P0643, P0652, P0653, P0661, P0662, P2088, P2089, P2090, P2091, P2096, P2097, P2100, P2101, P2122, P2123, P2127, P2128, P2176, P2297, P2301, P2303, P2304, P2306, P2307, P2309, P2310, P2A00, P2A0 are not set.
* The engine speed is greater than 1 200 RPM for a minimum of 2 s.
* The vehicle speed is less than 1.24 MPH.
* The intake mass air flow (MAF) is between 2.00-7.00 g/s.
* The vehicle is in closed loop.
* The calculated exhaust mass gas flow is between 5-55.56 g/s, and stable.
* The calculated catalyst temperature is between 480-800°C (896-1 472°F).
* The rear heated oxygen sensor (HO2S) has exceeded the dew point for more than 60 s.
* This diagnostic attempts one test during each period when the above conditions have been met. This diagnostic attempts up to 4 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 6 test attempts which will require at least 2 drive cycles. However, this diagnostic may require as many as 8 test attempts. Depending on driving conditions, more than 2 drive cycles may be required. Each test attempt may conclude within approximately 1 min.
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
Inspect for the following conditions, which may cause a catalyst 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 [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Control Module References 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.
2. Verify the following conditions do not exist with the catalyst:
* Dents
* A severe discoloration caused by excessive temperatures
* Road damage
* An internal rattle caused by damaged catalyst subset
* Restrictions
• If a condition is found, replace the catalyst
3. Verify the following conditions do not exist with the exhaust system:
* Leaks
* Physical damage
* Loose or missing hardware
* Properly torqued B52A Heated Oxygen Sensor 1 or B52B Heated Oxygen Sensor 2
• If a condition is found, repair the exhaust system.
• If the DTC fails this key cycle, continue with this procedure.
4. Verify the following conditions do not exist with the B52B Heated Oxygen Sensor 2.
* A grounded B52B Heated Oxygen Sensor 2 wiring harness
* Damage
• If a condition is found, replace the B52B Heated Oxygen Sensor 2.
5. If no physical condition is detected and the B52B Heated Oxygen Sensor 2 is as active as the B52A Heated Oxygen Sensor 1 after operating the engine at 1 500 RPM for 1 min and then returning to a stabilized idle, then replace the catalyst.
Repair Instructions
Note:
A new converter with less than 160 km (100 mi) on it may set DTC P0420 due to outgassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 h may correct the condition.
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Heated Oxygen Sensor Replacement - Sensor 1 Heated Oxygen Sensor Replacement - Sensor 1
* Heated Oxygen Sensor Replacement - Sensor 2 Heated Oxygen Sensor Replacement - Sensor 2
* Catalytic Converter Replacement (LUV) Catalytic Converter Replacement (LUV)
* Exhaust Leakage Exhaust Leakage
* Symptoms - Engine Exhaust Symptoms - Engine Exhaust