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.
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)
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)
Chevrolet Silverado 2500HD · 1999–2025
The transfer case encoder motor on the Silverado 2500HD (NP246/NP261/NP263 transfer cases) fails, preventing the vehicle from shifting between 2WD, 4WD High, and 4WD Low. The encoder motor is mounted on the outside of the transfer case and uses an electric motor with a position sensor to actuate the shift fork. Moisture ingress, corrosion, and worn motor brushes cause intermittent or complete failure. The "Service 4WD" message appears on the DIC, and the transfer case may get stuck in one mode. Failure is more common in salt-belt states.
Common Symptoms
- "Service 4WD" message on dashboard
- Transfer case will not shift out of 2WD
- Transfer case stuck in 4WD
- Grinding noise when attempting to shift transfer case
- 4WD indicator light flashing
- Clunking when shifting between 2WD and 4WD
How to Fix
Replace the transfer case encoder motor ($100-$250 for parts, $100-$200 labor). The motor is externally mounted on the transfer case and accessible from underneath the vehicle. Also inspect and replace the transfer case wiring connector if corroded — moisture wicking up the connector wires is a common cause of encoder motor failure. After replacement, use a scan tool to relearn the encoder motor position. Apply dielectric grease to the electrical connector to prevent future moisture ingress.
What you need to diagnose it
The repair instructions explicitly call for reading stored codes. Use a scanner that can read the named code families before choosing a repair.This issue involves C codes, which a basic engine-code reader cannot see.The recommended scanner supports these code families; confirm your exact year, model and module coverage before buying.
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Reading and clearing the code is DIY work. Module replacement or reprogramming is not — most modules are VIN-programmed, so a new one does nothing until a shop codes it to your car. Check for an open recall or service bulletin before buying anything.
Sources for this issue (1)
Chevrolet Colorado · 2004–2022
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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.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.