Unable to Perform Shift (GM)
The C0387 code means the vehicle's onboard diagnostic system has detected: Unable to Perform Shift (GM). This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $150 - $900 (encoder motor, switch, or wiring in the transfer-case control system)
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Common Symptoms
- Service 4WD message or light
- 4WD may not engage or disengage
- Possible binding in turns if stuck engaged
Probable Causes (Ranked by Likelihood)
- Fault in the four-wheel-drive/transfer case component this code names (Unable to Perform Shift) High
- Damaged wiring or a corroded connector in that circuit - road-splash zones corrode connectors High
- Failed related sensor or actuator Moderate
- Control module fault Low
Frequently Asked Questions
What does C0387 mean?
C0387 is a chassis code used primarily by GM vehicles: Unable to Perform Shift. It concerns the four-wheel-drive/transfer case system.
Can I keep driving with C0387?
Generally yes; the four-wheel-drive/transfer case system may be degraded. Diagnose soon, and treat any brake- or steering-related behavior change as urgent.
Is C0387 the same on every make?
The decimal C0xxx range is dominated by GM's assignments (Chevrolet, GMC, Buick, Cadillac). Other makes may use this ID differently - if your vehicle is not a GM product, verify the meaning in your make's service information.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Read the code with a GM-capable scan tool and note the symptom byte/subcode if shown.
-
View live data for the named circuit (e.g. all four wheel speeds while rolling for wheel-speed codes).
-
Inspect the circuit's wiring and connectors - chassis harnesses live in the splash zone and corrode first.
-
Follow the GM pinpoint test for C0387 before replacing components.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
Commonly Affected Vehicles
- Chevrolet, GMC, Buick, Cadillac (GM chassis code range)
Related Codes
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