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Tahoe / Yukon Service Manual

DTC P0421

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5471155 Diagnostic Instructions Perform the Diagnostic System Check prior to using this diagnostic procedure: Diagnostic System Check - Vehicle Review the description of Strategy Based Diagnosis: Strategy Based Diagnosis An overview of each diagnostic category can be found here: Diagnostic Procedure Instructions DTC Descriptor DTC P0421 Catalytic Converter Low Efficiency Circuit Description The main function of the close coupled diesel oxidation catalyst (CCDOC) is to control emissions of non methane hydrocarbons and carbon monoxide (CO). Its secondary function is to assist with the diesel particulate filter (DPF) regeneration, by obtaining and sustaining the temperature necessary for regeneration. In order to generate the high exhaust temperatures needed for regeneration, the aftertreatment system increases exhaust temperatures by injecting diesel fuel into the exhaust system via post-injection. The injected fuel is converted into heat by the CCDOC to incinerate soot accumulated in the DPF. The engine control module (ECM) monitors the exhaust gas temperature sensor 1 and 2 to determine if catalyst downstream temperatures are achieved during a DPF regeneration. Conditions for Running the DTC DTC P262B, U029E = Not set DTCs related to the following system/component = Not Set – B17 Barometric Pressure Sensor – B34 Engine Coolant Temperature Sensor – B65 Intake Manifold Pressure and Air Temperature Sensor – B74 Manifold Absolute Pressure Sensor – B75C Multifunction Intake Air Sensor – B115 Vehicle Speed Sensor – B131 Exhaust Temperature Sensor – B154 Diesel Particulate Filter Exhaust Differential Pressure Sensor – B195A Nitrogen Oxides Sensor 1 – Q14 Exhaust Gas Recirculation Valve – Q17 Fuel Injector Exhaust Gas Temperature Sensor 2 = Colder than 55°C (131°F) Coolant Temperature = Colder than 55°C (131°F) Engine » Running Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC Oxygen storage capacity of the catalyst = Less than a predefined threshold Actions Taken When the DTC Sets DTCs listed in the DTC Descriptor category = Type A DTC Conditions for Clearing the DTC DTCs listed in the DTC Descriptor category = Type A DTC Diagnostic Aids The continuing use of non ultra low sulfur fuel may be a contributor to diesel oxidation catalyst failure. Monitor may abort during very slow driving if catalyst heat up time is greater than 110 s Monitor may abort during aggressive driving after a cold start if catalyst heat up time is less than 32 s Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Master Electrical Component List 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 Verification

  1. Verify there are no DTCs set related to the following component/system: B17 Barometric Pressure Sensor B34 Engine Coolant Temperature Sensor B65 Intake Manifold Pressure and Air Temperature Sensor B74 Manifold Absolute Pressure Sensor B75C Multifunction Intake Air Sensor B115 Vehicle Speed Sensor B131 Exhaust Temperature Sensor B154 Diesel Particulate Filter Exhaust Differential Pressure Sensor B195A Nitrogen Oxides Sensor 1 Q14 Exhaust Gas Recirculation Valve Q17 Fuel Injector ⇒ If a related DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle. ⇓ If a related DTC is not set
  2. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
  3. Verify the DTC does not set. ⇒ If the DTC is set Refer to: Circuit/System Testing ⇓ If no DTC is set
  4. All OK. Circuit/System Testing
  5. Verify a condition does not exist with the component: Induction System — Leaking / Loose Clamps / Missing components / Restricted / Visible Damage Exhaust System — Leaking / Loose Clamps / Missing components / Restricted / Visible Damage » Refer to: Symptoms - Engine Exhaust for further diagnosis. ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  6. Verify the following conditions do not exist: Coolant consumption » Refer to: Loss of Coolant Fuel — Contaminated / Poor Quality » Refer to: Contaminants-in-Fuel Diagnosis Oil consumption » Refer to: Oil Consumption Diagnosis ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  7. Perform the scan tool function: Particulate Filter Service Regeneration
  8. Verify sensor 2 is at least 100°C (180°F) warmer than sensor 1: Exhaust Gas Temperature Sensor 1 Exhaust Gas Temperature Sensor 2 ⇒ If sensor 2 is not at least 100°C (180°F) warmer than sensor 1 Replace the component: Nitrogen Oxides Catalytic Converter — With Particulate Filter ⇓ If sensor 2 is at least 100°C (180°F) warmer than sensor 1
  9. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Verify the DTC does not set. ⇒ If the DTC sets Refer to step 1 ⇓ If no DTC is set
  10. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Nitrogen Oxides Catalytic Converter with Filter Replacement