Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P0595 Cruise Control Servo Control Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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. P0595 means the voltage in the servo supply or control circuit is too low – a short to ground or a missing 12 V source. As this supply feeds both valves, it is checked before P0583 or P0587. No manufacturer document available to us uses this code.

Likely causes

Supply line from brake switch to servo shorted to ground
Brake light switch (cruise contact)
Servo shorted internally
Engine module

Symptoms

  • Cruise control cannot be engaged or switches off
  • Cruise indicator goes out or flashes (depending on vehicle)
  • Usually no check engine light, code stored only

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–300
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

cruise control servobrake light switchservo wiringengine control module

Related codes

P0594P0596P0583P0587P0571

References: patents.google.com, patents.google.com, law.cornell.edu.