P0590 means the powertrain control module has detected that one of the cruise-control multifunction switch input circuits—labeled "B" by the manufacturer—is showing a continuous or implausible signal, as if a button is stuck or the circuit is electrically latched. The PCM compares the switch inputs against expected logic states; when one input remains active when it should change or be off, this code sets. It typically points to the steering-wheel-mounted cruise switches, the wiring that carries their signals, or the clockspring, rather than the engine computer itself.
The button assembly itself is the most common source. Internal contacts can short, corrode, or mechanically stick from age, heat, or liquid exposure, causing the PCM to see a constant input.
Because cruise-control signals pass through the rotating clockspring, broken or shorted ribbon circuits inside it can make the input appear stuck to the PCM.
A wire shorted to power or ground, or an open circuit in the steering column or dash harness, can hold the circuit at one voltage and trigger the stuck-circuit logic.
Liquid intrusion at the steering-wheel switch connector can bridge terminals, creating a constant signal that mimics a pressed or stuck button.
This is uncommon. Only consider the PCM after the switch, clockspring, and all wiring have tested good, because the module rarely fails for this specific input circuit.
Usually yes, but use caution. The main risk is unreliable cruise-control behavior, including a failure to cancel. Until the fault is repaired, avoid using cruise control.
No. PCM failure is genuinely rare for this code. In almost every case the problem is the cruise-control switch, the clockspring, or the wiring. Replacing the PCM first is usually the wrong repair.
You can do basic checks such as inspecting the buttons and retrieving codes. Testing the clockspring and airbag-related steering-wheel components requires proper safety precautions, so consult a service manual before proceeding.
The PCM monitors whether the switch input changes logically as buttons are pressed. A constant signal—whether from a physically stuck button, a shorted wire, or a failed clockspring—is interpreted as a stuck input rather than a simple open or short.