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Tahoe / Yukon Service Manual

DTC P1098 or P26BB

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5501087 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 P1098 Engine Coolant Control Valve Position Sensor Minimum Stop Performance DTC P26BB Engine Coolant Control Valve Performance Circuit/System Description For an overview of the component/system, refer to: Cooling System Description and Operation

Circuit Description
5 V Reference Regulated voltage supplied by the control module.
Serial Data Digitally encoded information for communication between devices.
Low Reference Grounded through the control module.
Component Description
K20 Engine Control Module The control module contains a microprocessor used to process input data to control outputs.
Q74 Engine Coolant Bypass Valve 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. The component is actuated by a bidirectional DC motor. Q74 is part of the component: Q97 Engine Coolant Flow Control Valve

The valve controls the distribution of coolant through the following components: Engine Oil Cooler Radiator Transmission Fluid Cooler Conditions for Running the DTC Conditions for Running the DTC P1098 DTCs related to the following system/component = Not Set B34B Engine Coolant Temperature Sensor 2 Q74 Engine Coolant Bypass Valve — Circuit Engine Coolant Temperature Sensor 2 = Warmer than −40°C (−40°F) Ignition and Start Switch Signal = On Frequency the DTC runs = Once — Per ignition cycle — After ignition Off — Within 1 min P26BB DTCs related to the following system/component = Not Set B34B Engine Coolant Temperature Sensor 2 Q74 Engine Coolant Bypass Valve — Circuit Ambient Air Temperature = Warmer than −20°C (−4°F) Engine Coolant Temperature Sensor 2 = Warmer than −20°C (−4°F) Ignition and Start Switch Signal = On Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC Desired Engine Coolant Bypass Valve Position = Learned Value Out of Range 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 Reference Information 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 U0617 is not set. ⇒ If DTC U0617 is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If DTC U0617 is not set
  3. Verify there are no DTCs set related to the following component/system: B34 Engine Coolant Temperature Sensor B66 Intake Air Temperature Sensor ⇒ If a related DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If a related DTC is not set
  4. Verify the coolant is at the correct level.
  5. Verify the following conditions do not exist: — Q74 Engine Coolant Bypass Valve Leaking » Refer to: Loss of Coolant Loose Clamps Missing components Visible Damage ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  6. Perform the scan tool control function: Engine Coolant Control Valve Mode — The value should increase and decrease according to the setting in the scan tool. Verify the component operates in both directions: Q74 Engine Coolant Bypass Valve ⇒ If the component does not work as specified Replace the component: Q74 Engine Coolant Bypass Valve ⇓ If the component works as specified
  7. 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 Replace the component: Q74 Engine Coolant Bypass Valve ⇓ If no DTC is set
  8. All OK. Repair Instructions Engine Coolant Flow Control Valve Replacement — Q74 Engine Coolant Bypass Valve Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification