P0420

DTC P0420

DTC DESCRIPTOR

DTC P0420
Catalyst System Low Efficiency

DIAGNOSTIC FAULT INFORMATION
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
A 3-way catalytic (TWC) converter 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, also referred to as the catalyst monitor sensor, 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, P2A03, or U0107 are not set.
- The engine has been running for more than 6 minutes.
- The engine speed has been more than 1200 RPM for more than 25 seconds.
- The engine speed is less than 1000 RPM.
- The engine coolant temperature (ECT) is between 70-125°C (158-257°F).
- The barometric pressure (BARO) is more than 70 kPa.
- The vehicle is in Closed Loop.
- The intake air temperature (IAT) is more than -20°C (-4°F).
- The battery voltage is more than 10.7 volts.
- The throttle position (TP) is less than 2.0 percent.
- The short term fuel trim (FT) is between -10 and +10 percent.
- The calculated TWC temperature (Calc. TWC Temp.) is between 385-640°C (725-1,184°F).
- The engine idle speed is stable.

CONDITIONS FOR SETTING THE DTC
- The ECM determines that the efficiency of the catalyst has degraded below a calibrated threshold.
- This diagnostic may conclude in as few as 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 7 minutes.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
- The following conditions may cause a catalytic converter to degrade:
- An engine misfire
- High engine oil or coolant consumption
- Retarded spark timing
- A weak or poor spark
- A lean fuel mixture
- A rich fuel mixture
- The following conditions may cause the catalyst test to abort:
- The vehicle falls outside the conditions for running the DTC.
- If 18 tests have been attempted, and the DTC has not run or passed during this key cycle, turn the key to OFF for 30 seconds. Perform the conditions for running a second time.

IMPORTANT: A new catalyst may fail this test due to out-gassing of the internal matting. If this occurs, operate the vehicle at highway speeds for approximately one hour and retest.

- If NO problems are found after performing circuit system testing, The catalyst may have been temporarily contaminated with a chemical from a fuel additive, fuel contamination, or any of the above conditions. If a contaminated catalyst is suspected, operate vehicle at highway speeds for 10 minutes and retest the converter.

CAUTION: Refer to Road Test Caution.

CIRCUIT/SYSTEM VERIFICATION
1. If any other DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis. Diagnostic Trouble Code Descriptions
2. Warm the catalyst by performing the following procedures:
- Fully open the hood.
- Place the transaxle in PARK for automatic transaxle.
- Place the transaxle is NEUTRAL for manual transaxle, with clutch pedal depressed.
- Set the parking brake.
- Press and hold the service brake.
3. Test the catalyst by performing the following procedures:
- Idle the engine and place the vehicle in Drive to activate the diagnostic. Within 60 seconds, the Cmmd. A/F Equivalence ratio will transition rich for up to 7 seconds, and then may transition lean for up to 7 seconds.
- Verify DTC P0420 has passed or failed this ignition cycle with the scan tool.
- This diagnostic attempts 1 test during each valid idle period once the above conditions have been met for 5 seconds. This diagnostic attempts up to 6 tests during each drive cycle. The first test may be run after the initial warm up period of 6 minutes. Maintain engine speed between 2,000-3,000 RPM in park or neutral for 2 minutes. Allow the engine to return to a stabilized idle. Shift into drive for an automatic transmission while applying the brake pedal firmly. Between each subsequent test, maintain engine speed between 2,000-3,000 RPM in park or neutral for 2 minutes. Allow the engine to return to a stabilized idle. Shift into drive for an automatic transmission, without touching the accelerator in order for the test to run. The catalyst diagnostic should conclude and pass or fail by the end of the 6 tests.

CIRCUIT/SYSTEM TESTING

NOTE:
- Refer to Heated Oxygen Sensor (HO2S) Resistance Learn Reset Notice.
- Refer to Three-Way Catalytic Converter Damage Notice.

1. Inspect the catalytic converter for the following conditions:
- Physical damage
- 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.
2. Inspect the exhaust system for the following conditions:
- Leaks before the converter
- Physical damage
- If a condition is found, replace the exhaust system, or components as necessary.
3. Inspect the HO2S 2 sensor and circuits for the following conditions:
- A grounded or chafing wiring harness
- Physical damage
- If a condition is found, replace the HO2S 2 sensor.
4. Inspect the HO2S 2 sensor for proper torque.
- If the HO2S 2 sensor has improper torque, correctly torque the sensor.
5. If no physical condition is detected perform the following:
- Clear all of the DTCs.
- Operate the vehicle under the conditions for running the DTC.
- If DTC P0420 runs, fails and illuminates the MIL, replace the catalytic converter.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Heated Oxygen Sensor (HO2S) Replacement Bank 1 Sensor 2
- Exhaust System Replacement
- Exhaust System Insulator, Hanger, Bracket Replacement
- Restricted Exhaust Verification Tests

REPAIR VERIFICATION
1. Warm the catalyst by performing the following procedures:
- Fully open the hood.
- Place the transaxle in PARK for automatic transaxle.
- Place the transaxle is NEUTRAL for manual transaxle, with clutch pedal depressed.
- Set the parking brake.
- Press and hold the service brake.
2. Test the catalyst by performing the following procedures:
- Idle the engine and place the vehicle in Drive to activate the diagnostic. Within 60 seconds, the Cmmd. A/F Equivalence Ratio will transition rich for up to 7 seconds, and then may transition lean for up to 7 seconds.
- Verify DTC P0420 has passed or failed this ignition cycle with the scan tool.
- This diagnostic attempts 1 test during each valid idle period once the above conditions have been met for 5 seconds. This diagnostic attempts up to 6 tests during each drive cycle. The first test may be run after the initial warm up period of 6 minutes. Maintain engine speed between 2,000-3,000 RPM in park or neutral for 2 minutes. Allow the engine to return to a stabilized idle. Shift into drive for an automatic transmission while applying the brake pedal firmly. Between each subsequent test, maintain engine speed between 2,000-3,000 RPM in park or neutral for 2 minutes. Allow the engine to return to a stabilized idle. Shift into drive for an automatic transmission, without touching the accelerator in order for the test to run. The catalyst diagnostic should conclude and pass or fail by the end of the 6 tests.