Cruise Control Multi-Function Input B Circuit High
The cruise control input signal to the engine computer is stuck at a high voltage, similar to a stuck gas pedal sensor that won't reset to zero. The ECU can't properly read the cruise control switch commands because the circuit is malfunctioning.
The ECM monitors the cruise control input circuit voltage, which should toggle between low and high states as buttons are pressed. When the voltage remains abnormally high and doesn't return to baseline, the ECU logs a fault. The circuit typically uses a pull-down resistor to ground, so a high voltage fault indicates either a short to power, open circuit, or stuck switch.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Cruise Control Input Voltage | 0.5V - 4.5V (variable with button presses) | Above 4.8V continuously or stuck high |
| Circuit Ground Connection | Less than 0.2V resistance to ground | Open or high resistance connection |
Code P0593 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0593 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.