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Tahoe / Yukon Service Manual

DTC P26C0, P26C2, P29FA, P29FB, U0618, or U111A

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5913123 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 P26C0 Engine Block Coolant Valve Stuck Open DTC P26C2 Engine Block Coolant Valve Stuck Closed DTC P29FA Engine Block Coolant Control Valve Position Sensor Circuit Low DTC P29FB Engine Block Coolant Control Valve Position Sensor Circuit High DTC U0618 Lost Communication with Engine Block Coolant Control Valve DTC U111A Lost Communication with Engine Coolant Bypass Valve Circuit/System Description For an overview of the component/system, refer to: Cooling System Description and Operation

Circuit Description
Ignition Supplied from a fuse.
Serial Data Digitally encoded information for communication between devices.
Ground Chassis Ground
Component Description
Q97B Engine Coolant Flow Control Valve - Block The component is actuated by a bidirectional DC motor. Q97B is part of the component: Engine Coolant Flow Control Valve
K20 Engine Control Module The control module contains a microprocessor used to process input data to control outputs. 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.

Conditions for Running the DTC Conditions for Running the DTC P26C0, P26C2 DTC P0689, P0690, P11C9, P117A, U111A = Not set { P26C0 } DTC P118A = Not set Engine Block Coolant Valve Position = −5 to 115° Ignition and Start Switch = Greater than 11 V Frequency the DTC runs = Continuously — After the running conditions are met P29FA, P29FB DTC P0689, P0690, P11C9, P117A, U111A = Not set { P29FA } Engine Block Coolant Valve Position = Less than −7° { P29FB } Engine Block Coolant Valve Position = Greater than 117° Ignition and Start Switch = Greater than 11 V Frequency the DTC runs = Continuously — After the running conditions are met U0618, U111A Ignition = On Ignition and Start Switch = Greater than 11 V Power Mode = Run Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC P26C0, P26C2, P29FA, P29FB Engine Block Coolant Valve Position = Not within a calibrated range U0618, U111A Serial Data circuit = Current 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 Schematic Reference Engine Heating/Cooling 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 DTC P26C0, P26C2, P29FA, P29FB, U111A is not set. ⇒ If DTC P26C0, P26C2, P29FA, P29FB, U111A is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If DTC P26C0, P26C2, P29FA, P29FB, U111A is not set
  2. Verify the coolant is at the correct level.
  3. Verify the following conditions do not exist: Q97B Engine Coolant Flow Control Valve - Block Leaking » Refer to: Loss of Coolant Missing components Stuck Closed Stuck Open Visible Damage ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  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 the DTC is not set
  5. All OK. Circuit/System Testing
  6. Ignition/Vehicle & All vehicle systems » Off
  7. Disconnect the electrical connector: Q97B Engine Coolant Flow Control Valve - Block
  8. Test for less than 10 Ω between the test points: Ground terminal 2 & Ground ⇒ If greater than 10 Ω 3.1. Disconnect the ground connection: G176A 3.2. Test for less than 2 Ω between the test points: Ground terminal 2 @ Component harness & G176A ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Repair the open/high resistance in the ground connection. ⇓ If less than 10 Ω
  9. Ignition » On / Vehicle » In Service Mode
  10. Verify a test lamp turns On between the test points: Ignition circuit terminal 3 & Ground ⇒ If the test lamp does not turn On and the circuit fuse is OK 5.1. Ignition/Vehicle » Off & Remove » Test lamp 5.2. Test for less than 2 Ω between the test points: Ignition circuit terminal 3 & Output terminal @ F88UA Fuse ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Verify the fuse is OK and there is voltage at the fuse. ⇒ If the test lamp does not turn On and the circuit fuse is open 5.1. Ignition/Vehicle » Off & Remove » Test lamp 5.2. Test for infinite resistance between the test points: Ignition circuit terminal 3 & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇒ If infinite resistance » Replace the component: Q97B Engine Coolant Flow Control Valve - Block ⇓ If the test lamp turns On
  11. Test for 8 to 10 V between the test points: Serial Data circuit terminal 1 @ Component harness & Ground ⇒ If greater than 10 V 6.1. Ignition/Vehicle » Off 6.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 6.3. Ignition » On / Vehicle » In Service Mode 6.4. Test for less than 1 V between the test points: Serial Data circuit terminal 1 @ Component harness & Ground ⇒ If 1 V or greater » Repair the short to voltage on the circuit. ⇒ If less than 1 V » Replace the component: K20 Engine Control Module ⇓ If less than 8 V 6.1. Ignition/Vehicle » Off 6.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 6.3. Test for infinite resistance between the test points: Serial Data circuit terminal 1 @ Component harness & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇓ If infinite resistance 6.4. Test for less than 2 Ω between the test points: Serial Data circuit terminal 1 @ Component harness & Terminal 105 X2 @ Control module harness ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Replace the component: K20 Engine Control Module ⇓ If between 8 and 10 V
  12. Test or replace the component: Q97B Engine Coolant Flow Control Valve - Block Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Engine Coolant Flow Control Valve Replacement — Q97B Engine Coolant Flow Control Valve - Block For control module replacement, programming, and setup refer to: Control Module References