Open circuit, damaged wiring or poor connection in the servo control circuit; Corroded, loose or pushed-out pins at the servo or module connector; Faulty cruise control servo or actuator with an open internal winding or motor; Blown fuse or relay feeding the cruise control circuit; Faulty brake or clutch switch input interfering with the cruise control circuit on some models; Fault inside the controlling module (engine or cruise control module); Outdated or faulty module software where the manufacturer has documented it as a cause.

P0594

Cruise Control Servo Control Circuit/Open.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
94: FaultThe specific fault in that area

What it means

P0594 is the generic SAE J2012 code for a fault in the cruise control servo control circuit, specifically an open circuit. The control module commands the cruise control servo or actuator and found no expected electrical response, so it has logged the fault and usually disables cruise control. How the servo is built and which module controls it varies by make and model.

Symptoms

Cruise control will not engage or cancels itself
Cruise control warning or indicator light on the dash
Engine management or check engine light may be on
Speed not held steady on a cruise set
Cruise control switch seems dead

Possible causes

Open circuit, damaged wiring or poor connection in the servo control circuitlikely
Corroded, loose or pushed-out pins at the servo or module connectorlikely
Faulty cruise control servo or actuator with an open internal winding or motorpossible
Blown fuse or relay feeding the cruise control circuitpossible
Faulty brake or clutch switch input interfering with the cruise control circuit on some modelspossible
Fault inside the controlling module (engine or cruise control module)rare
Outdated or faulty module software where the manufacturer has documented it as a causerare

How to diagnose

Read all stored codes and freeze frame data, and note whether other cruise, throttle or brake switch codes are present
Check the relevant fuses and relays against the wiring diagram for the specific model
Visually inspect the servo, its wiring and connectors for damage, corrosion, water ingress or chafing
Check the wiring loom for rubbing or stretching where it passes moving parts or the bulkhead
Test the servo supply, earth and control wires with a multimeter against the manufacturer wiring diagram
Check circuit continuity from the module to the servo, with the battery disconnected and the module unplugged where the procedure requires it
Measure servo resistance or test its operation with a suitable scan tool actuator test, following model-specific specs
Check for relevant manufacturer service bulletins or software updates for the vehicle

How to fix

Repair or replace damaged wiring and restore the open circuit
Clean, repair or replace corroded or damaged connectors and terminals
Replace the cruise control servo or actuator if it fails testing
Replace blown fuses or faulty relays after finding why they failed
Replace or update the controlling module only after wiring and servo have been confirmed good, and update software if a known fault applies

Can I keep driving?

Low severity

The car is normally safe to drive as only cruise control is usually lost. Book it in for repair at your convenience, but do not ignore it if other warning lights or throttle problems appear.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.