C0387: How to Diagnose & Fix — Manufacturer-Specific Chassis Code (commonly transfer case / shift-related on GM)
4 vehicles · 3 makes · $100-$700 repair
How to diagnose and fix C0387: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Cadillac Escalade ESV · 2002–2020
The transfer case encoder motor that controls AWD/4WD engagement fails, causing the "Service 4WD" message and preventing 4WD engagement. The position sensor inside the encoder motor sends incorrect signals. The transfer case may also develop an internal fluid leak past the front output seal.
Common Symptoms
- Service 4WD message on dash
- 4WD not engaging
- Grinding noise when shifting to 4WD
- Transfer case stuck between modes
How to Fix
Replace the encoder motor on the transfer case. The motor is externally mounted and accessible. After replacement, a transfer case relearn procedure must be performed with a scan tool. Check and top off the transfer case fluid with the correct Auto-Trak II fluid.
Sources for this issue (1)
GMC Jimmy · 1998–2001
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)
Chevrolet Colorado · 2004–2022
On four-wheel-drive Colorados the front axle uses an electric disconnect actuator on the front differential housing that must engage before the transfer case will complete a shift into 4HI/4AUTO/4LO. The actuator's motor, position sensor, and its exposed connector sit low on the axle where they take road spray, salt, and mud. Owners report the dash showing "Service 4WD", the 4WD selector lights blinking and then reverting to 2WD, and the truck driving in two-wheel drive despite the transfer case shifting. C0387 is the code most often stored. This is distinct from transfer case encoder motor failure: forum diagnosis threads repeatedly find the transfer case shifted correctly while the front axle actuator, its connector, or the chafed harness running to it was the actual fault. Reported on the 2004-2012 GMT355 trucks and again on the 2015-2022 generation, and it is much more common in road-salt states.
Common Symptoms
- Service 4WD message on the driver information center
- 4WD selector light blinks then returns to 2WD
- 4HI or 4AUTO will not engage
- Front wheels do not pull even though the transfer case shifted
- Grinding or clunk when attempting to engage 4WD
How to Fix
Diagnose before parts-swapping: scan for C0387 and check whether the transfer case actually shifted. Inspect the front axle actuator connector for green corrosion and the harness where it routes along the axle/frame for chafing - a repaired harness or cleaned/repinned connector fixes a large share of cases for the cost of a connector kit. If the actuator itself is at fault, replace it (about $150-$350 for the part) and relearn/verify engagement; note that owners have reported receiving new actuators that only engage part-way, so verify engagement physically rather than by dash light. No recall covers this.
Sources for this issue (3)
Chevrolet Silverado 2500HD · 1999–2025
Find C0387 by make
Browse every documented model and issue for your make.
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?
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.
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?
Repair costs for C0387 range from $100 to $700, depending on the vehicle and root cause.
Which vehicles are affected by C0387?
Au7o has documented C0387 across 4 vehicle models from 3 manufacturers: Cadillac, Chevrolet, GMC.
Join 600+ people using Au7o to better understand their vehicles.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.