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Tahoe / Yukon Service Manual

DTC P17D4, P215B, or P279A-P279C

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 P17D4 Transfer Case Neutral Range Detected in High or Low Range DTC P215B Vehicle Speed Sensor and Output Shaft Speed Sensor Correlation DTC P279A Transfer Case High Range Incorrect Ratio DTC P279B Transfer Case Low Range Incorrect Ratio DTC P279C Transfer Case High or Low Range Detected in Neutral Range Symptom Byte Information: Symptom Byte List Circuit/System Description For an overview of the component/system, refer to: Transfer Case Description and Operation The ECM uses the following to determine the transfer case mode.

  1. Compares the transmission output speed (Transmission OSS) to the vehicle speed (Vehicle Speed Sensor) to calculate transfer case range/ratio.
  2. LAN message sent by the transfer case shift control module to the ECM indicating transfer case range. The ECM uses the transfer case range to determine engine torque required and transmission shift schedule. The internal fault detection is handled inside the control module. No external circuit diagnosis is involved. Conditions for Running the DTC Engine = Running — For greater than 5 s Vehicle Speed = 10 to 200 km/h (6 to 124 MPH) Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC The ECM detects a mismatch between the calculated transfer case ratio and the TCCM transfer case range message. The ECM has detected 32 fail counts out of 400 samples. Frequency the DTC runs = Continuously — After the running conditions are met Actions Taken When the DTC Sets No additional actions taken Conditions for Clearing the DTC The conditions for setting the DTC no longer exist. A history DTC will clear after 40 consecutive malfunction-free ignition cycles. Diagnostic Aids The Actions Taken for P279A may set DTC P16F3. DTC P279A, P279B, or P279C may set before P0502, P0503, P0721, P0722, P0723, P077C, P077D, P2160, P2161. When attempting to set ECM internal DTCs, run the engine for at least 1 min, and then shut the engine off for 2 min. Following this procedure will allow for a complete ECM shutdown. Program the ECM with the latest software version and retest the DTC to see if the DTC resets. Reference Information Schematic Reference Transfer Case Control 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 Scan Tool Reference Control Module References Circuit/System Verification
  3. Ignition » On / Vehicle » In Service Mode
  4. Verify there are no other DTCs set, except for DTC P17D4, P215B, P279A, P279B, P279C. ⇒ If any other DTCs are set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If no other DTCs are set
  5. Operate the vehicle within the Conditions for Running the DTC. Verify the scan tool parameter: Transmission OSS — The value should change smoothly and gradually as the vehicle speed is increased and decreased. ⇒ If the value does not change smoothly and gradually Refer to the appropriate diagnostic procedure listed below: { MQC } — Refer to: DTC P0721-P0723, P077C, P077D, P172A, or P172B ⇓ If the value changes smoothly and gradually
  6. Operate the vehicle within the Conditions for Running the DTC. Verify the scan tool parameter: Vehicle Speed Sensor — The value should change smoothly and gradually as the vehicle speed is increased and decreased. ⇒ If the value does not change smoothly and gradually Refer to: DTC C0500-C0504, C0506-C0510, or C0512-C0516 ⇓ If the value changes smoothly and gradually
  7. Program the ECM.
  8. Operate the vehicle within the Conditions for Running the DTC.
  9. Verify the DTC does not set. ⇒ If the DTC sets 7.1. Replace the component: K20 Engine Control Module 7.2. Program the ECM. 7.3. Operate the vehicle within the Conditions for Running the DTC. 7.4. Verify the DTC does not set. ⇒ If the DTC sets Mechanical Malfunction — Refer to: Transfer Case Disassemble ⇓ If no DTC is set All OK. ⇓ If no DTC is set
  10. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification For control module replacement, programming, and setup refer to: Control Module References