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Tahoe / Yukon Service Manual

DTC P026C or P026D

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5398961 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 P026C Fuel Injection Quantity Too Low DTC P026D Fuel Injection Quantity Too High Circuit/System Description For an overview of the component/system, refer to: Exhaust Aftertreatment System Description Fuel System Description

Component Description
B195 Nitrogen Oxides Sensor NOx sensors work similar to wide-band O2 sensors. The sensors consist of two measuring cells. In the first cell, an electric pump current is used to separate out the oxygen in the exhaust. The NOx remains and is conveyed into the second chamber. Here a second pump current decomposes the NOx into nitrogen and oxygen. The oxygen concentration is measured and from there the NOx concentration can be calculated.
K20 Engine Control Module The control module controls a series of actuators to ensure optimal engine performance. The control module does this by reading values from a variety of sensors, interprets the data and adjusts the engine actuators accordingly.
Q17 Fuel Injector Fuel injectors are solenoid valves that inject fuel either into the intake system or directly into the cylinder. The amount of fuel injected depends on the length of the electrical pulse that is applied.

Conditions for Running the DTC DTCs related to the following system/component = Not Set – B14A Automatic Transmission Output Speed Sensor – B14C Automatic Transmission Input Speed Sensor – B17 Barometric Pressure Sensor – B26 Crankshaft Position Sensor – B34 Engine Coolant Temperature Sensor – B65 Manifold Absolute Pressure and Intake Air Temperature Sensor – B75 Mass Airflow Sensor – R29 Fuel Filter – Fuel System Ambient Air Temperature = Warmer than −20°C (−4°F) Barometric Pressure Sensor = Greater than 70 kPa (10.2 PSI) Engine Speed = 1,100 to 1,800 RPM Engine Coolant Temperature Sensor = Warmer than 45°C (113°F) Ignition and Start Signal = Greater than 11 V Low Fuel Indicator = Off Transmission = In Gear — Not in Park or Neutral Vehicle Speed Sensor = 30 to 140 km/h (19 to 87 MPH) Frequency the DTC runs = Once — Per drive cycle — After the running conditions are met — For greater than 10 s Conditions for Setting the DTC P026C Fuel Injection Quantity = Less than a predefined threshold — For greater than 10 s P026D Fuel Injection Quantity = Greater than a predefined threshold — 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 A malfunction in the following components may also cause DTC P026C, P026D to set: – B75 Mass Airflow Sensor – Q14 Exhaust Gas Recirculation Valve – B195A Nitrogen Oxides Sensor 1 The following conditions could cause DTC P026C, P026D to set: – B65 Manifold Absolute Pressure and Intake Air Temperature Sensor — Flow Restricted – Q14 Exhaust Gas Recirculation Valve — Binding or Sticking – Fuel — Contamination Modifications to the intake air systems may cause this DTC to set. 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: B14A Automatic Transmission Output Speed Sensor B14C Automatic Transmission Input Speed Sensor B17 Barometric Pressure Sensor B26 Crankshaft Position Sensor B34 Engine Coolant Temperature Sensor B48 Fuel Temperature Sensor B65 Manifold Absolute Pressure and Intake Air Temperature Sensor B75 Mass Airflow Sensor Fuel System ⇒ If a related DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If a related DTC is not set
  2. Ignition » On / Vehicle » In Service Mode
  3. Verify the scan tool parameter: Mass Airflow Sensor = 0 to 2 g/s ⇒ If not between 0 and 2 g/s Refer to: DTC P0101 ⇓ If between 0 and 2 g/s
  4. Engine » Running
  5. Verify the scan tool parameter: Mass Airflow Sensor = 5 to 40 g/s ⇒ If not between 5 and 40 g/s 5.1. Verify the following conditions do not exist: B75 Mass Airflow Sensor — Contamination of the measuring element / Water intrusion Intake Air Duct — Cracked / Leaking / Loose Clamps / Restrictions / Visible Damage ⇒ If a condition exists » Repair or replace as necessary ⇒ If no condition exists » Refer to: Particulate Filter Service Regeneration ⇓ If between 5 and 40 g/s
  6. Verify the following conditions do not exist: . B65 Manifold Absolute Pressure and Intake Air Temperature Sensor — Flow Restricted Q14 Exhaust Gas Recirculation Valve — Binding or Sticking ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  7. Verify a condition does not exist with the component: Exhaust System — Leaking / Missing components / Restricted » Refer to: Exhaust Leakage ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  8. Perform the following procedure/test: Cylinder Power Balance Test Verify the procedure/test passes. ⇒ If the procedure/test does not pass Replace the component that failed the test: Q17 Fuel Injector ⇓ If the procedure/test passes
  9. Test or replace the component: B195A Nitrogen Oxides Sensor 1 Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification High Pressure Diesel Fuel Injector Replacement Nitrogen Oxides Sensor Replacement - Position 1