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Tahoe / Yukon Service Manual

DTC P0171 or P0172

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5456258 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 P0171 Fuel Trim System Lean DTC P0172 Fuel Trim System Rich Circuit/System Description For an overview of the component/system, refer to: Fuel System Description Conditions for Running the DTC DTC P262B = Not set DTCs related to the following system/component = Not Set – B9 Ambient Air Temperature Sensor – B17 Barometric Pressure Sensor – B34 Engine Coolant Temperature Sensor – B66 Intake Air Temperature Sensor – B115 Vehicle Speed Sensor Ambient Air Temperature = Warmer than −20°C (−4°F) Barometric Pressure = Greater than 70 kPa (10.2 PSI) Engine = Running Engine Coolant Temperature = Warmer than 45°C (113°F) Fuel level = Greater than 10% Ignition Voltage = Greater than 11 V NOx Sensor 1 Heater Operation = Allowed Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC The limit to correct a rich air/fuel ratio has been exceeded. — After the running conditions are met — For greater than 10 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 aftermarket devices which may affect the operation of the system. 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. Ignition » On / Vehicle » In Service Mode
  2. Verify DTC P262B is not set. ⇒ If the DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If the DTC is not set
  3. Verify there are no DTCs set related to the following component/system: B9 Ambient Air Temperature Sensor B17 Barometric Pressure Sensor B34 Engine Coolant Temperature Sensor B66 Intake Air Temperature Sensor B115 Vehicle Speed Sensor ⇒ If a related DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If a related DTC is not set
  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. Verify the DTC does not set. ⇒ If the DTC sets Refer to: Circuit/System Testing ⇓ If no DTC is set
  5. All OK. Circuit/System Testing
  6. Engine » Idling — At normal operating temperature
  7. Verify the scan tool parameter: Mass Airflow Sensor = 5 to 40 g/s ⇒ If less than 5 g/s Verify the following conditions do not exist: 2.1. Induction System — Leaking / Restricted » Refer to: Component/System Leak Test ⇒ If a condition exists Repair or replace as necessary ⇒ If no condition exists Perform the scan tool function: Particulate Filter Service Regeneration ⇒ If greater than 40 g/s Verify the following conditions do not exist: 2.1. Induction System — Leaking » Refer to: Component/System Leak Test ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists Refer to step 3 ⇓ If between 5 and 40 g/s
  8. Ignition/Vehicle » Off
  9. Verify a condition does not exist with the component: Exhaust System — Leaking Refer to: Symptoms - Engine Exhaust ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  10. Perform the following procedure/test: Cylinder Power Balance Test ⇒ If the procedure/test does not pass Repair as necessary ⇓ If the procedure/test passes
  11. Replace the component: B195A Nitrogen Oxides Sensor 1 Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Nitrogen Oxides Sensor Replacement - Position 1 Additional Procedures Nitrogen Oxides Sensor Reset — Perform only when the following component/system is replaced or serviced: B195A Nitrogen Oxides Sensor 1