Cruise Control Servo Control Circuit / Open
The cruise control servo motor circuit has lost electrical connection or power, like a telephone line going dead. Your cruise control system can't receive commands to maintain speed.
The ECM monitors voltage and current flow to the cruise control servo motor circuit. It expects proper voltage supply and a complete circuit path to the actuator. An open circuit or missing voltage triggers the fault code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Servo Motor Circuit Voltage | 12V supply present with continuity | 0V, open circuit, or voltage drop below threshold |
| Servo Motor Current Draw | Normal amperage during operation | No current flow or circuit open detected |
Code P0594 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, P0594 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.