Wiring fault in the servo control circuit, such as a short to voltage or chafed insulation; Corroded, loose or damaged connector at the servo or control unit; Faulty cruise control servo or actuator with an internal electrical fault; Low or unstable system voltage from a weak battery or charging fault; Faulty brake or clutch switch input interfering with cruise control operation; Internal fault in the engine control unit or cruise control module driver circuit.

P0596

Cruise Control Servo Control Circuit High.

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
96: FaultThe specific fault in that area

What it means

P0596 means the engine control unit has detected a high voltage or signal condition in the control circuit for the cruise control servo (the actuator that operates the throttle or speed control). The control unit monitors this circuit and sets the code when the measured state does not match what it commanded, such as a short to voltage. How the servo is fitted and driven depends on the vehicle, and many modern cars use electronic throttle control instead of a separate servo.

Symptoms

Cruise control will not engage or drops out unexpectedly
Cruise control indicator light flashing or not illuminating
Engine management warning light on
Cruise control speed hunting or surging while active
Normal driving unaffected apart from loss of cruise function

Possible causes

Wiring fault in the servo control circuit, such as a short to voltage or chafed insulationlikely
Corroded, loose or damaged connector at the servo or control unitlikely
Faulty cruise control servo or actuator with an internal electrical faultpossible
Low or unstable system voltage from a weak battery or charging faultpossible
Faulty brake or clutch switch input interfering with cruise control operationpossible
Internal fault in the engine control unit or cruise control module driver circuitrare

How to diagnose

Read all stored codes and freeze frame data, noting any other cruise, throttle or brake switch codes
Check battery condition and charging voltage, as low or erratic voltage can cause circuit faults
Visually inspect the servo, its wiring and connectors for damage, chafing, water ingress and corrosion
Check the brake and clutch switch operation and their wiring, as these feed the cruise control system
Back-probe the servo control circuit with a multimeter and compare voltage and ground readings to the manufacturer wiring diagram
Check for a short to voltage by testing the harness between the servo and control unit with the connectors disconnected
Test the servo resistance or operation against the manufacturer specification, as the method varies by model
Clear the code and road test to see if it returns

How to fix

Repair or replace damaged wiring and re-secure the harness away from heat and sharp edges
Clean or replace corroded or damaged connectors and terminals
Replace the cruise control servo or actuator if it fails testing
Restore correct charging and battery condition if system voltage is faulty
Replace a faulty brake or clutch switch
Repair or replace the control unit only after the wiring and servo have been proven good, following manufacturer procedure

Can I keep driving?

Low severity

The car can normally be driven as the fault mainly affects cruise control. Book it in for diagnosis soon, and avoid using cruise control until it is repaired.

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