The automatic transmissions are equipped with gear solenoids that allow the transmission fluid to advance through the interior channels. This creates the necessary pressure to change speed.
Diagnostic code P0751 OBDII shows that a vehicle controller module has found the “A” shift solenoid to have performance problems or there is a blockage of the solenoid. If the Powertrain Control Module (PCM) detects that there are differences in the actual transmission ratio compared to the anticipated ratio due to engine speed, throttle position, and other factors that determine it.