OBD-II code P0790 indicates a malfunction in the Normal/Performance Switch Circuit, which is used by the transmission control module (TCM) to detect the driver's selected driving mode. When the TCM detects an implausible signal or open/short circuit from this switch, it sets this code and may default to a single shift pattern.
The switch itself may be worn, contaminated, or internally shorted, causing an incorrect or no signal to the TCM.
Wiring between the mode switch and the TCM can chafe, break, or short to ground/power, leading to circuit malfunctions.
Corroded, loose, or bent pins at the switch connector or TCM connector can cause intermittent or high-resistance faults.
Internal TCM failure is possible but less common; it may misinterpret switch signals or have damaged input circuits.
Rarely, the PCM (if it handles transmission control) may have an internal fault, but this should only be considered after all other causes are ruled out.
Yes, the vehicle is usually drivable, but you may be limited to a single shift mode and could experience harsh shifting or reduced fuel economy. It's best to address the issue promptly to avoid potential transmission stress.
No, this code is almost never caused by an internal transmission mechanical failure. It is typically an electrical issue with the mode switch, wiring, or connectors.
No, control module failure is rare for this code. The most common causes are a faulty mode switch or wiring problems. Replacing the PCM or TCM without thorough diagnosis is often a misdiagnosis.
Unlikely, but low system voltage or electrical noise can sometimes cause erratic sensor readings. Check battery and charging system health if other electrical issues are present.