P0593 indicates that the cruise control module is receiving a voltage signal from the multi-function input B circuit that is higher than expected. This typically points to a problem with the switch or its wiring rather than the engine control module.
The switch integrated in the steering wheel or stalk can develop an internal short, causing a high voltage signal on the circuit.
Damaged insulation or abrasion in the harness can create a continuous high voltage reference, triggering the code.
Poor contact can intermittently elevate the signal voltage, especially under vibration or temperature changes.
Movement of the vehicle may temporarily create a high voltage condition that sets the code when the fault occurs.
A genuine PCM malfunction is possible but is uncommon; it typically only occurs after other components have been ruled out.
No. The PCM is rarely the cause; most often the issue is a faulty switch or wiring problem.
A blown fuse would create an open circuit, not a high voltage condition, so it is not a typical cause of P0593.
The vehicle can be driven normally; cruise control will simply not function, and the code does not affect drivability or emissions.
Keep the switch and wiring protected from moisture and physical damage, and inspect connectors regularly for signs of corrosion or looseness.