P0594 indicates the cruise‑control servo control circuit has an open electrical path, meaning the engine control module cannot drive the servo to maintain speed. This is typically caused by a faulty component, broken wiring, or a missing power/ground rather than a computer problem. The code triggers a check‑engine light and disables cruise‑control operation.
The servo’s internal motor windings can open, preventing the unit from receiving or delivering the required electrical signal.
A break, cut, or pinched wire in the cruise‑control circuit creates an open that the ECM cannot close.
If the fuse or relay that supplies power to the servo is open, the circuit cannot complete.
Switches that command cruise on/off or cancel can develop an open contact, breaking the control circuit.
Moisture or oxidation can increase resistance or open the connection at the servo’s plug.
The engine computer itself can fail to drive the circuit, but this is far less common than external wiring or component issues.
No. In most cases the problem is in the servo, wiring, fuse, relay, or switches. PCM failure is an uncommon cause, so replacement is usually unnecessary and not recommended until those items are ruled out.
Yes, the car will run normally, but cruise control will be disabled. You should have the fault diagnosed and repaired to restore the feature.
When the control circuit is open, the ECM cannot activate the system, so the indicator either stays off or flashes to signal a fault.
Intermittent opens are often due to a loose connector, a wire that flexes and breaks under movement, or corrosion that worsens with temperature and moisture.