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Tahoe / Yukon Service Manual

DTC P261F, P2B86, P2B87, P3077, P3078, U0623, or U137E

DTC P261F, P2B86, P2B87, P3077, P3078, U0623, or U137E 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 P261F Auxiliary Coolant Pump Stuck On DTC P2B86 Auxiliary Coolant Pump Overspeed DTC P2B87 Auxiliary Coolant Pump Underspeed DTC P3077 Auxiliary Coolant Pump Low Speed DTC P3078 Auxiliary Coolant Pump High Speed DTC U0623 Lost Communication with Auxiliary Coolant Pump DTC U137E Invalid Data Received from Heater Coolant Pump Circuit/System Description For an overview of the component/system, refer to: Cooling System Description and Operation

Circuit Description
B+ Supplied from a fuse.
Serial Data Digitally encoded information for communication between devices.
Ground Chassis Ground
Component Description
G17 Heater Coolant Pump The auxiliary heater coolant pump circulates engine coolant through the HVAC heater core when the mechanical coolant pump is not operating.
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
Component Description
sensors, interprets the data and adjusts the engine actuators accordingly.

Conditions for Running the DTC P261F Auxiliary Coolant Pump = Commanded Off Ignition = On Ignition Voltage = Greater than 11 V No other DTCs related to the concerned component are set. Frequency the DTC runs = Continuously — After the running conditions are met P2B86, P2B87, P3077, P3078 Ignition = On or Engine = Running Ignition Voltage = Greater than 11 V No other DTCs related to the concerned component are set. Frequency the DTC runs = Continuously — After the running conditions are met U0623, U137E Ignition = On Ignition Voltage = Greater than 11 V Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC P261F Auxiliary Coolant Pump = Commanded state does not match the actual state — For greater than 8 s P2B86, P2B87 Auxiliary Coolant Pump Speed = Not within a calibrated range — For greater than 8 s P3077, P3078 Auxiliary Coolant Pump Speed = Not within a calibrated range — For greater than 4 s U0623 Serial Data circuit = Communication Failed — For greater than 2.5 s U137E Serial Data circuit = Message Counter Incorrect — Control module that has set the DTC The above condition(s) must occur 3 times. 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. DTCs related to the following system/component = Not Set B34 Engine Coolant Temperature Sensor ⇒ If a related DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If a related DTC is not set
  2. Ignition/Vehicle » Off
  3. Verify the following conditions do not exist: G17 Heater Coolant Pump — Abnormal noise / Leaking / Loose Clamps / Visible Damage Air Pocket @ Cooling System » Refer to: Cooling System Draining and Filling Antifreeze Concentration — Incorrect » Refer to: Cooling System Draining and Filling Hoses / Lines @ Cooling System — Kinked / Leaking / Restricted / Visible Damage Hoses / Lines @ G17 Heater Coolant Pump — Kinked / Leaking / Restricted / Visible Damage Incorrect fluid level or condition — Coolant @ Surge Tank » Refer to: Loss of Coolant ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  4. Ignition » On / Vehicle » In Service Mode
  5. Verify DTC U137E is not set and no other DTCs are set. ⇒ If DTC U137E is set and no other DTCs are set Replace the component: G17 Heater Coolant Pump
  6. Verify DTC U0623 is not set. ⇒ If DTC U0623 is set Refer to: Circuit/System Testing ⇓ If the DTC is not set
  7. Verify DTC P261F, P2B86, P2B87, P3077, P3078 is not set. ⇒ If any of the DTCs are set Replace the component: G17 Heater Coolant Pump ⇓ If none of the DTCs are set
  8. 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
  9. All OK. Circuit/System Testing
  1. Ignition/Vehicle & All vehicle systems » Off
  2. Disconnect the electrical connector: G17 Heater Coolant Pump
  3. Test for less than 10 Ω between the test points: Ground terminal 1 & Ground ⇒ If greater than 10 Ω 3.1. Disconnect the ground connection: G117 3.2. Test for less than 2 Ω between the test points: Ground terminal 1 @ Component harness & The other end of the circuit @ Ground connection G117 ⇒ 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
  4. Verify a test lamp turns On between the test points: B+ circuit terminal 2 & Ground ⇒ If the test lamp does not turn On and the circuit fuse is OK 4.1. Remove » Test Lamp 4.2. Test for less than 2 Ω between the test points: Ignition circuit terminal 2 @ Component harness & Output terminal @ F80UA 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 4.1. Remove » Test Lamp 4.2. Test for infinite resistance between the test points: Ignition circuit terminal 2 & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇒ If infinite resistance » Replace the component: G17 Heater Coolant Pump ⇓ If the test lamp turns On
  5. Ignition » On / Vehicle » In Service Mode
  6. Test for 8 to 10 V between the test points: Serial Data circuit terminal 3 @ 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 3 @ 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 3 @ 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 3 @ Component harness & The other end of the circuit @ 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
  7. Test or replace the component: G17 Heater Coolant Pump Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Heater Coolant Pump Replacement — G17 Heater Coolant Pump For control module replacement, programming, and setup refer to: Control Module References