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DTC P0420 or P0430 (LF1, LFW)

DTC P0420 or P0430 (LF1, LFW)

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


DTC Descriptor

DTC P0420

Catalyst System Low Efficiency Bank 1

DTC P0430

Catalyst System Low Efficiency Bank 2

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, 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 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, P0018, P0019, P0053, P0054, P0059, P0060, P0068, P0090, P0091, P0092, P00C8, P00C9, P00CA, P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0135, P0137, P0138, P013A, P013B, P013C, P013D, P013E, P013F, P0140, P0141, P014A, P014B, P0151, P0152, P0153, P0155, P0157, P0158, P0160, P0161, P0171, P0172, P0174, P0175, P0191, P0192, P0193, P0222, P0223, P0300, P0301. P0302, P0303, P0304, P0305, P0306, P0335, P0336, P0341, P0345, P0346, P0365, P0366, P0390, P0391, P0443, P0506, P0507, P0606, P1153, P16F3, P2101, P2122, P2123, P2127, P2128, P2135, P2138, P2227, P2228, P2229, P2230, P2270, P2271, P2272, or P2273 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 965 RPM

- The engine run time is greater than a calibrated value

- Both conditions exist for greater than 15 s

• The throttle is in the rest position.

• The intake air temperature (IAT) is between -20 to +250°C (-4 to +482°F).

• The ignition voltage is greater than 11 V.

• The engine coolant temperature (ECT) is between 40-127°C (104-261°F).

• The barometric pressure (BARO) is greater than 70 kPa.

• The engine has been idling less than 50 s.

• The vehicle speed is less than 2 km/h (1 mph).

• The short term fuel trim is learned.

• The air flow into the engine is between 3-13 g/s.

• The EVAP purge concentration is learned.

• The catalytic converter (TWC) calculated temperature is between 450-850°C (842-1,562°F).

• 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 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 and P0430 are Type A DTCs.

Conditions for Clearing the DTC

DTC P0420 and P0430 are Type A DTCs.

Diagnostic Aids

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

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification


1. Observe the DTC information with a scan tool. Verify there are no other DTCs set.

2. If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle

3. Operate the vehicle in the conditions that triggered the DTC. Check that the scan tool's parameter Catalyst Monitor Not At Idle Test Conditions is met. The parameter will change to Yes when the Conditions have been met.

4. If not the specified value, operate the vehicle within the Conditions for Running the DTC.

5. When the parameter has changed to Yes and 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 parameters will increment by one and the Catalyst Monitor Test Result parameters will indicate Pass, Fail or No Decision.

10. If no decision has been made, repeat steps 2-6 until the Test Result parameters indicate Pass or Fail.


Circuit/System Testing


1. Verify the following conditions do not exist with the appropriate 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.

2. Verify the following conditions do not exist with the exhaust system:

• Leaks

• Physical damage

• Loose or missing hardware

• If a condition is found, repair the exhaust system.

3. Verify the following conditions do not exist with the appropriate HO2S 2:

• The HO2S is not at the correct torque

• Damage

• If a condition is found, replace the HO2S 2 as necessary.

4. If all physical conditions test normal, test or replace the catalytic converter.


Repair Instructions

Note

A new converter with less than 100 miles on it may set DTC P0420 or P0430 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.



• Exhaust Leakage

• Restricted Exhaust

• Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 (LF1)

• Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 (LF1)

• Perform the HO2S Heater Learn procedure with a scan tool after replacing the Heated Oxygen an HO2S has been replaced.

• Catalytic Converter Replacement - Left Side (LF1)

• Catalytic Converter Replacement - Right Side (LF1)


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 in the conditions that triggered the DTC. Check that the scan tool's parameter Catalyst Monitor Not At Idle Test Conditions is met. The parameter will change to Yes when the Conditions have been met.

6. If not the specified value, operate the vehicle within the Conditions for Running the DTC.

7. When the parameter has changed to Yes and 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 parameters will increment by one and the Catalyst Monitor Test Result parameters will indicate Pass, Fail, or No Decision.

12. If no decision has been made, repeat steps 5-9 until the Test Result parameters indicate Pass or Fail.

13. If the repair was related to a DTC, duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to the Diagnostic Trouble Code (DTC) List - Vehicle