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P0748 is a transmission fault code which indicates linear solenoid electrical failure. Possible causes for this code to set are:
Short or open in wiring
TCM (Transmission Control Module) internal malfunction
Linear solenoid valve malfunction
Ensure all appropriate connections are clean and tight. If the wiring is OK then the most likely culprit would be the linear solenoid valve. It is very rare and unlikely to have a TCM failure.