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 controls emissions of hydrocarbons, CO and NOx. The catalyst within the converter promotes a chemical reaction, which oxidizes the hydrocarbons and the CO that are present in the exhaust gas. This process converts the hydrocarbons and the CO into water vapor and CO2, and reduces the NOx, by converting the NOx into nitrogen. The catalytic converter also stores oxygen. The ECM monitors this process by using a Heated Oxygen Sensor (HO2S) that is in the exhaust stream after the 3-way catalytic converter. 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 3-way catalytic converter. 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
* DTC P0016, P0017, P0030, P0036, P0053, P0054, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0114, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P013A, P013B, P013E, P013F, P0140, P0141, P015A, P015B, P16F3, P0171, P0172, P0222, P0223, P0300, P0301, P0302, P0303, P0304, P0335, P0336, P0340, P0341, P0365, P0366, P0443, P0502, P0503, P0506, P0507, P0606, P0697, P06A3, P2101, P2122, P2123, P2127, P2128, P2135, P2138, P2270 or P2271 is not set.
* Before the ECM performs the idle test, the vehicle must be driven under the following conditions:
- The engine speed is greater than 1,100 RPM for a minimum of 5 s.
- The vehicle speed is less than 2 km/h (1.24 mph).
- The engine runtime is greater than 120 s.
* The run/crank voltage is greater than 11 V.
* The intake air temperature (IAT) is between -20 to +250°C (-4 to +482°F).
* The engine coolant temperature (ECT) is between 40-140°C (104-284°F).
* The engine has been idling less than 50 s.
* The short term fuel trim is between -20 to +30.
* The barometric pressure (BARO) is greater than 70 kPa.
* The intake mass air flow (MAF) is between 1.50-7.00 g/s.
* The engine is operating in closed loop.
* The calculated catalyst temperature is between 550-950°C (1,022-1,742°F).
* The automatic transmission is in drive range.
* 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
Inspect for the conditions listed below, 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
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 Verification
1. Ignition ON.
2. Verify there are no other DTCs set.
• If a DTC is set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
• If a DTC is not set
3. Operate the vehicle within the Conditions for Running the DTC.
4. Verify the scan tool Catalyst Monitor Not At Idle Test Conditions Met parameter changes to Yes.
• The parameter does not change to Yes
Operate the vehicle within the Conditions for Running the DTC.
• The parameter changes to Yes
5. When the conditions are safe, stop and idle the vehicle in gear.
6. Apply the service brake.
7. Monitor the scan tool Catalyst Monitor Test State parameter. When the parameter indicates Active, the Catalyst Monitor Test is running.
8. Continue to monitor the parameter. When the parameter indicates Inactive, the Catalyst Monitor Test has completed.
9. When the test has completed, the Catalyst Monitor Test Counter parameter will increment by one and the Catalyst Monitor Test Result parameter will indicate Passed, Failed or No Result.
• The parameter indicates No Result
Repeat steps 3-8 until the Test Result parameter indicates Passed or Failed
• The parameter indicates Failed
Refer to Circuit /System Testing
• The parameter indicates Passed
10. All OK.
Circuit/System Testing
1. Verify the conditions listed below do not exist with the catalytic converter:
* Dents
* Severe discoloration caused by excessive temperatures
* Road damage
* Internal rattles caused by damaged catalyst substrate
* Restrictions
• If a condition is found
Replace the catalytic converter
• If no condition is found
2. Verify the conditions listed below do not exist with the exhaust system:
* Leaks
* Physical damage
* Loose or missing hardware
• If a condition is found
Repair or replace the affected component as necessary.
• If no condition is found
3. Verify the conditions listed below do not exist with the B52B Heated Oxygen Sensor 2:
* The HO2S is not at the correct torque
* Damage
• If a condition is found
Replace the B52B Heated Oxygen Sensor 2 or repair the condition as necessary.
• If no condition is found
4. Test or replace the catalytic converter.
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.
* Heated Oxygen Sensor Replacement - Sensor 2 Heated Oxygen Sensor Replacement - Sensor 2
Repair Verification
1. Install any components that have been removed or replaced during diagnosis.
2. Perform any adjustments, programming or setup procedures that are required when a component is removed or replaced.
3. Clear the DTCs with a scan tool.
4. Turn OFF the ignition for 60 s
5. Operate the vehicle within the Conditions for Running the DTC.
6. Verify the scan tool Catalyst Monitor Not At Idle Test Conditions Met parameter changes to Yes.
• The parameter does not change to Yes
Operate the vehicle within the Conditions for Running the DTC.
• The parameter changes to Yes
7. When the conditions are safe, stop and idle the vehicle in gear.
8. Apply the service brake.
9. Monitor the scan tool Catalyst Monitor Test State parameter. When the parameter indicates Active, the Catalyst Monitor Test is running.
10. Continue to monitor the parameter. When the parameter indicates Inactive, the Catalyst Monitor Test has completed.
11. When the test has completed, the Catalyst Monitor Test Counter parameter will increment by one and the Catalyst Monitor Test Result parameter will indicate Passed, Failed or No Result.
• The parameter indicates No Result
Repeat steps 5-10 until the Test Result parameters indicate Passed or Failed
• The parameter indicates Failed
Refer to Circuit /System Testing
• The parameters indicates Pass
12. All OK.