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DTC P0420 (LLU)

DTC P0420 (LLU)

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 00

Catalyst System Low Efficiency

Circuit/System Description

Note

A new converter with less than 160 km (100 mi) on it may set DTC P0420 00 due to outgassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 h may correct the condition.


A 3 way catalytic converter controls emissions by converting hydrocarbons and carbon monoxide (CO) into carbon dioxide (CO2), and oxides of nitrogen (NOX) into nitrogen. The 3 way catalytic converter also stores oxygen. When the listed driving conditions are met, the catalyst system efficiency test will run. The engine control module (ECM) monitors this oxygen storage capacity by comparing the pre- and post-catalyst oxygen sensor signals while adding and subtracting fuel during specific driving conditions. The ECM compares the pre- and post-catalyst oxygen sensor signals to determine if the oxygen storage capacity of the catalyst is degraded.

Conditions for Running the DTC


• DTC P0030 00, P0031 00, P0032 00, P0036 00, P0037 00, P0038 00, P0100 00, P0101 00, P0102 00, P01013 00, P0121 00, P0122 00, P0123 00, P0130 00, P0131 00, P0132 00, P0133 00, P0134 00, P0135 00, P0136 00, P0137 00, P0138 00, P0140 00, P0141 00, P0171 00, P0172 00 P0221 00, P0222 00, P0223 00, P0300 00, P0301 00, P0302 00, P0303 00, P0304 00, P0313 00, P0420 00, P0444 00, P0459 00, P1138 00, P2096 00, P2097 00, P2197 00, P2188 00, P2270 00 and P2271 00 is not set.

• The engine speed is between 1400-3200 RPM.

• The evaporative emission (EVAP) purge concentration is learned.

• The engine load is between 15-50%.

• The vehicle is in closed loop.

• The calculated exhaust mass gas flow is between 5-55.56 g/s, and stable.

• The engine coolant temperature (ECT) at engine start is colder than -10.5°C (+50.9°F)

• The ambient temperature is more than -15°C (+5°F).

• The heated oxygen sensor 2 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 00 is a Type A DTC.

Conditions for Clearing the DTC

DTC P0420 00 is a Type A DTC.

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

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

Refer to Three-Way Catalytic Converter Damage Caution .

Refer to Heated Oxygen Sensor Resistance Learn Reset Caution .


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

2. If any of the DTCs are 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 subset

• 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

• Properly torqued B52A Heated Oxygen Sensor 1 or B52B Heated Oxygen Sensor 2

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

6. If the DTC fails this key cycle, continue with this procedure.

7. 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.

8. 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 1500 RPM for 1 min and then returning to a stabilized idle, then replace the catalytic converter.


Repair Instructions

Note

A new converter with less than 160 km (100 mi) on it may set DTC P0420 00 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 after completing the diagnostic procedure.


• Heated Oxygen Sensor Replacement - Sensor 2

• Catalytic Converter Replacement (LAU/A28NER) Catalytic Converter Replacement (LBY/A20DTR) Catalytic Converter Replacement (LLU/A16LET) Catalytic Converter Replacement (LBS/A20DTH) Catalytic Converter Replacement (LHU/A20NFT) Catalytic Converter Replacement (LHU/A20NFT - AWD)

• Exhaust Leakage

• Symptoms - Engine Exhaust