Circuit/System Verification

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.

Verify that the TREC fuse, and the Miscellaneous IGN fuse, underhood fuse block, are NOT open.
- If the TREC fuse is OPEN
  Test the battery positive voltage circuit, K69 transfer case control module harness X3, terminal C, for a short to ground. Refer to Testing for Short to Ground .
- If the Miscellaneous IGN fuse is OPEN
  Test the ignition 1 voltage circuit, K69 transfer case control module harness X2, terminal 6, for a short to ground. Refer to Testing for Short to Ground .
- Go to next step: If the TREC fuse and the Miscellaneous IGN fuse are NOT open
Ignition ON, engine OFF.
Verify no other DTC's are set. If any other DTC's are set, diagnose them first.
Verify DTC C0387 is only set as a history DTC.
- If DTC C0387 is set as current
  Refer to Circuit/System Testing below.
- Go to next step: If DTC C0387 is set as history
Visually inspect each connector terminal of the K69 transfer case control module and the A16 transfer case motor connector for damage or corrosion. Repair as necessary.
NOTE: After inspection, apply Nyogel lubricant 760G to each connector terminal. Ensure each connector and CPA is correctly seated.
Clear DTC C0387 from history.
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 C0387 sets
  Refer to Circuit/System Testing below.
- Go to next step: If DTC C0387 does not set
All OK.