If your vehicle is showing gear indicator light (prndl) is flashing on the dash, here are the most likely causes and the parts you'll need to fix each one.
The sensor that tells the computer which gear you have selected is failing or out of alignment. The computer flashes the PRNDL lights because it is receiving conflicting signals about what gear the transmission is actually in.
Low fluid levels or extremely dirty fluid can cause internal pressure drops and slipping. The transmission computer detects this abnormal operation and flashes the indicator to warn you to stop driving.
The transmission relies on input and output speed sensors to know exactly when to shift. If a sensor fails, the computer detects a mismatch in expected speeds and triggers a warning light.
Shift solenoids direct hydraulic fluid to change gears. If one gets stuck or fails electrically, the transmission cannot shift properly, causing the gear indicator to flash and often locking the car into a single gear (limp mode).
The computer that controls the transmission has failed, lost communication, or is experiencing a software glitch, leading to erratic shifting and flashing gear indicator lights.