Code P0748 indicates an electrical fault in the pressure control solenoid 'A' circuit. The transmission control module (TCM) or powertrain control module (PCM) has detected an open, short, or other circuit malfunction in the solenoid that regulates line pressure for shift feel and engagement.
The solenoid itself may have an internal open or short circuit, often due to age, heat, or contamination, causing incorrect resistance readings.
Chafed, broken, or corroded wires and terminals between the PCM/TCM and the solenoid can cause intermittent or permanent open/short circuits.
Moisture intrusion, dirt, or vibration can lead to poor electrical contact at the solenoid connector, triggering the code.
Insufficient fluid level or degraded fluid can cause the solenoid to work harder, overheat, and fail electrically, or trigger false circuit codes.
An internal driver failure in the control module is possible but far less common than solenoid or wiring issues; should only be considered after exhaustive testing.
It is not recommended. The transmission may be in limp mode, limiting operation to one gear, which can cause overheating and further damage if driven for extended periods.
Replacing the solenoid is often the correct fix, but only after verifying that the wiring, connectors, and fluid are in good condition. Skipping diagnosis can lead to unnecessary parts replacement.
Almost never. The vast majority of P0748 faults are caused by a failed solenoid or wiring issue. Control module failure is rare and should only be considered after all other possibilities are ruled out.
If the code was triggered by low or dirty fluid causing the solenoid to malfunction, a fluid change may help, but the underlying electrical fault usually requires solenoid or wiring repair.