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Tahoe / Yukon Service Manual

DTC P18A1, P18AA, P18AB, or P27EC

Automatic Transmission - 10L80 MHS MQC | Diagnostic Information and Procedures | Document ID: 5224815 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 P18A1 Electronic Transmission Range Select Valve Performance - Stuck On DTC P18AA Transmission Range Control Valve Position Sensor Circuit Stuck On DTC P18AB Transmission Range Control Valve Position Sensor Circuit Stuck Off DTC P27EC Transmission Range Control Valve Position Sensor Circuit Performance Diagnostic Fault Information

Component DTC Condition
Transmission Control Solenoid Valve 8 P18A1, P18AA, P18AB, P27EC Binding or Sticking / Stuck
Control Valve Body Electronic Transmission Range Select (ETRS) Valve P18A1, P18AA, P18AB, P27EC Oil Channels or Orifices — Blocked by debris / Restricted Valve — Binding or Sticking / Stuck

Circuit/System Description For an overview of the component/system, refer to: Electronic Component Description Conditions for Running the DTC { P18A1 } DTC P18AA, P18AB, P27EC = Not set { P18AA } DTC P18AB, P27EC = Not set { P18AB } DTC P18AA, P27EC = Not set { P27EC } DTC P18AA, P18AB = Not set DTCs related to the following system/component = Not Set — B315A Transmission Range Control Valve 1 Position Switch Battery Voltage = Greater than 9 V Engine = Running High Side Driver 1 & High Side Driver 2 = On Ignition and Start Signal = 9 to 32 V Ignition and Start Switch Signal = On Conditions for Setting the DTC B315A Transmission Range Control Valve 1 Position Switch = Commanded state does not match the actual state — For greater than 1 s Actions Taken When the DTC Sets DTCs listed in the DTC Descriptor category = Type A DTC Autostart/Autostop = Disabled — If equipped Line Pressure Command = Default 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. Verify the condition does not exist: Incorrect fluid level or condition » Refer to: Transmission Fluid Level and Condition Check ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  2. Ignition » On / Vehicle » In Service Mode
  3. Perform the following action: Clear the DTCs.
  4. Road test the vehicle. » Refer to: Road Test
  5. DTCs related to the following system/component = Not Set — B315A Transmission Range Control Valve 1 Position Switch ⇒ If a related DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇒ If DTC P18A1, P18AA, P18AB, P27EC is set Refer to: Diagnostic Fault Information ⇓ If no DTC is set
  6. 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 DTC P18A1, P18AA, P18AB, P27EC is set Refer to: Diagnostic Fault Information ⇓ If no DTC is set
  7. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Control Valve Body Replacement For control module replacement, programming, and setup refer to: Control Module References