P0594Cruise Control Servo Control Circuit/Open
- Generic OBD-II code · Powertrain
- How the car detects it
- Older engines without electronic throttle use a vacuum cruise servo on the throttle cable: a vacuum valve (closed when unpowered) opens the throttle with intake vacuum, a vent valve (open when unpowered) holds or releases it, and a dump valve fed through the brake switch vents it when braking. Where the engine module drives these valves, it checks each circuit and switches cruise off; CARB treats this as emission-neutral, usually without warning lamp. P0594 concerns the servo control or supply circuit: an open circuit. Where the servo is fed through the cruise contact of the brake light switch, braking interrupts this supply on purpose, so the brake switch and its wiring are typical causes and brake lights may be affected too. No manufacturer document available to us describes P0594 in detail.
- What you may notice
- Cruise control cannot be engaged or switches off
- Usually no check engine light, code stored only
- Possibly brake light problem as well (shared switch)
- Likely causes
- LikelyBrake light switch (cruise contact) faulty or misadjusted
- PossibleSupply line open or shorted to ground
- PossibleServo connector or servo
- RareEngine module output
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.