C0387 Unable to Perform Shift

Definition

Common causes

• Faulty transmission control module (TCM)
• Malfunctioning shift solenoid
• Wiring issues or damaged connectors
• Low transmission fluid level or fluid contamination
• Faulty transmission position sensor
• Mechanical transmission issues
• Software or calibration issues in the TCM
• Electrical shorts or open circuits in the transmission system

Common misdiagnoses

• Transmission fluid issues
• Faulty transmission control module (TCM)
• Wiring or connector problems
• Faulty shift solenoids
• Incorrectly calibrated throttle position sensor
• Engine control module (ECM) issues
• Mechanical transmission problems
• Faulty vehicle speed sensor (VSS)
• Issues with the gear selector or linkage
• Battery or charging system problems

Troubleshooting steps

1. 1. Check for Additional Codes

   Use an OBD-II scanner to check for any other trouble codes that may be present. Addressing all related codes can help pinpoint the issue

2. 2. Inspect Wiring and Connectors

   Examine the wiring and connectors related to the transmission control module and shift solenoids. Look for signs of damage, corrosion, or loose connections

3. 3. Check Transmission Fluid

   Ensure that the transmission fluid is at the correct level and in good condition. Low or dirty fluid can cause shifting issues. If the fluid is dirty, consider changing it

4. 4. Inspect the Shift Solenoids

   The shift solenoids control the flow of transmission fluid and are critical for proper shifting. Test the solenoids for proper operation and replace any that are faulty

5. 5. Examine the Transmission Control Module (TCM)

   The TCM may be malfunctioning. Check for software updates or reprogramming needs. In some cases, replacing the TCM may be necessary

6. 6. Check for Mechanical Issues

   Inspect the transmission for any mechanical problems, such as worn gears or clutches. A transmission rebuild or replacement may be required if significant damage is found

7. 7. Test the Battery and Charging System

   A weak battery or charging system can cause erratic behavior in electronic components, including the transmission control system. Ensure the battery is in good condition and fully charged

8. 8. Perform a Reset

   Sometimes, clearing the codes and resetting the system can resolve temporary issues. After clearing the codes, take the vehicle for a test drive to see if the code returns

9. 9. Consult Technical Service Bulletins (TSBs)

   Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues and fixes

10. 10. Seek Professional Help

    If the issue persists after performing these steps, it may be best to consult a professional mechanic or a transmission specialist for further diagnosis and repair. Always remember to follow safety precautions when working on vehicles, and if you're unsure about any step, it's best to seek professional assistance