Circuit/System Testing

WARNING: This page is about a different car, the 2018 GMC Yukon XL, 2018 GMC Yukon, 2018 Chevrolet Tahoe, and 2018 Chevrolet Suburban. However, it is still accessible from the selected car via links, so may be relevant.

Install scan tool.
Wheel speed sensors:
1. Take the vehicle on a short test drive on a smooth and level road.
2. Verify that, when at a steady speed, all of the front and rear speed sensors parameters do not vary or become intermittent.
- If while driving at a steady speed the RPM values vary or become intermittent
  check the K17 Electronic Brake Control Module for wheel speed DTC's. Wheel speed DTC diagnostics are in antilock brake systems.
- Go to next step: If all of the front and rear speed sensors parameters do not vary or become intermittent
Transfer case clutch integrity:
1. Shift the vehicle into 4WD High/Locked and take it for a test drive. Clear the DTC if possible.
2. Verify that while under heavy acceleration that the front and rear wheel speeds are similar.
- If the front wheel speeds are much lower
  this indicates a weak clutch and a transfer case disassembly and inspection will be required. Refer to Transfer Case Disassemble .
- Go to next step: If the front and rear wheel speeds are similar
A16 transfer case motor - brake/lock:
1. Clear DTC's. Using the S77 Transfer Case Shift Control Switch function of the scan tool, shift the vehicle to 2WD range.
2. Monitor the Transfer Case Motor Amperage parameter in the Data Display feature of the scan tool.
3. Using the S77 Transfer Case Shift Control Switch function of the scan tool, command the transfer case to the 4WD High/Locked range.
4. Verify that the Transfer Case Motor Amperage parameter increases while the motor is shifting, and then returns to 0 amps within 5 seconds or less.
- If the amperage stays high longer than 5 seconds
  this indicates the brake is not holding. Replace the A16 Transfer Case Motor. Refer to Transfer Case Two/Four Wheel Drive Actuator Replacement .
- Go to next step: If the amperage increases while the motor is shifting, and then return to 0 amps within 5 seconds or less
Mechanical binding:
1. Engage parking brake.
2. Block rear wheels.
3. Lift front wheels.
4. Ignition ON, engine OFF. Install scan tool.
5. Transfer case in 2WD. Transmission in Neutral.
6. Using the Front Axle Engagement Actuator control function, engage the front axle.
7. Verify that the front prop shaft turns while holding one front tire stationary and spinning the other tire.
- If the front prop shaft does not turn
  inspect the front axle clutch fork for mechanical binding. Refer to Four-Wheel Drive Does Not Disengage .
- Go to next step: If the front prop shaft turns
If all prior evaluations test normal:
1. Reprogram the K69 Transfer Case Control Module. Refer to Control Module References .
2. Perform the Range Actuator Learn procedure in the Control Functions feature of the scan tool. Refer to Transfer Case High/Low Clutch Reset .
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. The DTC should not set.
- If DTC C0397 sets
  replace the K69 Transfer Case Control Module and perform the Range Actuator Learn procedure. Refer to Transfer Case Control Module Replacement and Transfer Case High/Low Clutch Reset .
- Go to next step: If DTC C0397 does not set
All OK.