Circuit/System Verification

WARNING: This page is about a different car, the 2023 GMC Sierra 3500 HD and 2023 GMC Sierra 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.

Ignition - On/Vehicle - In Service Mode
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
- Go to next step: If no other DTCs are set
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, or P172A
- Go to next step: If the value changes smoothly and gradually
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, C0512-C0516, C050A, or C050C-C050F
- Go to next step: If the value changes smoothly and gradually
Program the ECM.
Operate the vehicle within the Conditions for Running the DTC.
Verify the DTC does not set.
- If the DTC sets
1. Replace the component: K20 Engine Control Module
2. Program the ECM.
3. Operate the vehicle within the Conditions for Running the DTC.
4. Verify the DTC does not set.
  - If the DTC sets
    Mechanical Malfunction - Refer to: Transfer Case Disassemble (with MYD) , or Transfer Case Disassemble (with MGM, MGU)
  - Go to next step: If no DTC is set
    Go to next step: All OK.
- Go to next step: If no DTC is set
All OK.