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DTC P0420 or P0430 (LAU)

DTC P0420 or P0430 (LAU)

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 the amount of 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

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.


• DTC P0010, P0011, P0013, P0014, P0030, P0031, P0032, P0036, P0053, P0097, P0098, P0100, P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0128, P0130, P0131, P0132, P0133, P0135, P0137, P0138, P013A, P0140, P0141, P0221, P0222, P0223, P0300, P0335, P0336, P0341, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0458, P0459, P0461, P0496, P0502, P0506, P0507, P167A, P2088, P2089, P2090, P2091, P2096, P2097, P2176, P2195, P2196, P2232, P2237, P2243, P2251, P2270, P2271, P2297, or P2626 is not set.

• The engine speed is between 1,040-2,760 RPM.

• The engine load is between 15-50 %.

• The engine is operating in Closed Loop.

• The calculated exhaust mass gas flow is between 5-56 g/s, and stable.

• The calculated catalyst temperature is between 400-850°C (852-1,562°F).

• The intake air temperature (IAT) is greater than -15°C (5°F).


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 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 Testing


1. Engine idling, observe the DTC information with a scan tool. Verify there are no HO2S or misfire DTCs set.

2. If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnosis the applicable DTC, before proceeding with this diagnostic procedure.

3. 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.

4. 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.

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

• The HO2S is not at the correct torque

• Damage

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

6. Engine idling, increase engine speed to 1,500 RPM for 1 minute and then return to a stabilized idle. Check HO2S 1 and 2 voltage parameters with a scan tool. HO2S 1 voltage should be more active than for HO2S 2.

7. If HO2S 2 is as active as HO2S 1, 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.


Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• 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 an HO2S has been replaced.

• Catalytic Converter Replacement - Left Side (LF1)

• Catalytic Converter Replacement - Right Side (LF1)