Possible reasons:
Mechanical problems:
* Worn or damaged gear shift actuator
*Damaged or broken reverse gear solenoid
* Worn or damaged planetary gear
*Low transmission fluid level
* Problems with the gearshift position sensor
Electrical problems:
* Faulty reverse gear solenoid
*Blown or damaged fuse
*Wiring problems
Electronic problems:
*Transmission control module (TCM) malfunction
* Problems with TCM software
Steps to resolve the issue:
1. Check the transmission fluid level: Low fluid levels can cause problems with gear shifting. Bring the fluid level to normal.
2. Check the condition of the reverse gear solenoid: Diagnose the solenoid using a scanner or multimeter. Replace it if necessary.
3. Check the fuses: Locate the fuse for the reverse gear and check for a blown fuse. Replace the fuse if necessary.
4. Check the condition of the shift lever position sensor: Ensure that the sensor is properly calibrated and is sending the correct signal to the TCM.
5. Perform TCM diagnostics: Use a scan tool to check for trouble codes related to the TCM or reverse gear solenoid. Clear the codes and retest.
6. Contact a mechanic: If self-diagnosis and repairs do not work, contact a qualified mechanic. They may need to disassemble the transmission for further diagnosis and repair.