C0387 on GMC: How to Diagnose & Fix
Manufacturer-Specific Chassis Code (commonly transfer case / shift-related on GM)
1 GMC model · 1 documented issue · $150-$400 repair
C0387 on GMC by model: symptoms, diagnosis and fix
The NP136 AutoTrac transfer case encoder motor fails, preventing the system from engaging 4WD or switching between 2WD and 4WD modes. The "Service 4WD" message illuminates on the dash.
Common Symptoms
- Service 4WD light
- Cannot engage 4WD
- Grinding from transfer case
- 4WD indicator light flashing
How to Fix
Replace the encoder motor (Dorman 600-102) mounted on the transfer case. Drain and refill the transfer case with Auto-Trak II fluid during the repair. Clear DTCs after replacement.
Sources for this issue (1)
C0387 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does C0387 mean on a GMC?
C0387 stands for "Manufacturer-Specific Chassis Code (commonly transfer case / shift-related on GM)." C0387 is a manufacturer-specific chassis code that falls in a range largely reserved/non-standardized under SAE, so its exact meaning varies by manufacturer. On many GM vehicles it appears alongside transfer-case encoder/shift codes and is generally associated with an inability to complete a requested shift or a related transfer-case/electronic shift fault. Because the precise definition is not standardized, the code should be confirmed against the specific vehicle's service information. In general it points to a chassis driveline or shift-control concern rather than the engine itself. On GMC it is documented across 1 model: Jimmy.
What are the most common causes of C0387?
The most common causes of C0387 are: Transfer case encoder motor or shift fault (GM applications), Damaged or corroded wiring/connectors in the affected circuit, Failed shift motor or actuator, Control module (e.g., transfer case control module) fault, Low system voltage or poor ground, Mechanical binding in the shift mechanism. The specific cause varies by vehicle.
How much does it cost to fix C0387 on a GMC?
Published repair estimates on GMC range from $150 to $400 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for C0387 on a different make?
View C0387 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.