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Tahoe / Yukon Service Manual

DTC P0401 or P049B

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5982097 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 P0401 Exhaust Gas Recirculation Valve Flow Insufficient DTC P049B Exhaust Gas Recirculation Valve 2 Insufficient Flow Circuit/System Description For an overview of the component/system, refer to: Exhaust Gas Recirculation (EGR) System Description The engine control module can not directly measure the amount of recirculated exhaust gases. To verify the correct operation of the recirculation system, it uses a compare between the fresh air that was measured by the mass air flow sensor and the calculated amount that the engine is expected to suck in. The difference is the amount of recirculated exhaust. Conditions for Running the DTC P0401 DTC P262B = Not set DTCs related to the following system/component = Not Set – B9 Ambient Air Temperature Sensor – B26 Crankshaft Position Sensor – B34 Engine Coolant Temperature Sensor – B65 Intake Manifold Pressure and Air Temperature Sensor – B75C Multifunction Intake Air Sensor – B115 Vehicle Speed Sensor – Q17 Fuel Injector Ambient Air Temperature = Warmer than -20°C (−4°F) Barometric Pressure = Greater than 69.6 kPa (10.1 PSI) Engine Coolant Temperature = Warmer than 70°C (158°F) Fuel Control Loop Status = Closed Loop Ignition Voltage = Greater than 11 V Frequency the DTC runs = Continuously — After the running conditions are met — For greater than 12.5 s P049B DTC P262B = Not set DTCs related to the following system/component = Not Set – B9 Ambient Air Temperature Sensor – B34 Engine Coolant Temperature Sensor – B65 Intake Manifold Pressure and Air Temperature Sensor – B75C Multifunction Intake Air Sensor – B115 Vehicle Speed Sensor Ambient Air Temperature = Warmer than -7°C (19°F) Barometric Pressure = Greater than 74.8 kPa (10.8 PSI) Engine Coolant Temperature = Warmer than 70°C (158°F) Fuel Control Loop Status = Closed Loop Ignition Voltage = Greater than 11 V Frequency the DTC runs = Continuously — After the running conditions are met — For greater than 9 s Conditions for Setting the DTC Mass Air Flow = Not within a calibrated range — For greater than 12.5 s Actions Taken When the DTC Sets DTCs listed in the DTC Descriptor category = Type B DTC Conditions for Clearing the DTC DTCs listed in the DTC Descriptor category = Type B DTC Diagnostic Aids Inspect for the following conditions: Inspect for aftermarket devices which may affect the operation of the system. MAF Sensor — Contamination of the measuring element MAF Sensor — Skewed Intake Air Duct — Restricted 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 Circuit/System Verification

  1. Verify there are no DTCs set related to the following component/system: B9 Ambient Air Temperature Sensor B26 Crankshaft Position Sensor B34 Engine Coolant Temperature Sensor B65 Intake Manifold Pressure and Air Temperature Sensor B75C Multifunction Intake Air Sensor B115 Vehicle Speed Sensor M122 Exhaust Pressure Control Valve Actuator 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. Verify the following conditions do not exist: Air Cleaner Element — Restricted / Saturated with water EGR Cooler — Restricted EGR Valve 1 / EGR Valve 2 — Binding or Sticking / Restricted / Visible Damage Exhaust Gas Recirculation System — Leaking / Restricted Exhaust System — Leaking / Missing components / Restricted / Visible Damage Induction System — Leaking / Restricted » Refer to: Charge Air Cooler Diagnosis Mass Air Flow Sensor — Contaminated / Skewed Throttle Body — Binding or Sticking / Restricted Turbocharger — Leaking / Restricted ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  3. Clear the DTCs.
  4. 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.
  5. Verify the DTC does not set. ⇒ If the DTC sets Replace the appropriate component: Q14A Exhaust Gas Recirculation Valve 1 / Q14B Exhaust Gas Recirculation Valve 2 ⇓ If no DTC is set
  6. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Exhaust Gas Recirculation Valve Replacement - Exhaust Manifold — Q14A Exhaust Gas Recirculation Valve 1 Exhaust Gas Recirculation Valve Replacement - Exhaust Gas Recirculation Cooler — Q14B  Exhaust Gas Recirculation Valve 2