P0594Generic code

P0594 Code: Cruise Control Servo Control Circuit/Open

The P0594 code means the cruise control servo circuit is open, so the part gets no current when it is commanded on. It can leave you with cruise control that does not work. Check the fuse, relay, connector and wiring before replacing anything.

Severity
Low
Can I keep driving?
Yes, no immediate risk
Estimated cost
$50 to $400
Difficulty
Medium
System
Idle and Speed Control
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0594 code means

The cruise control servo moves the throttle to hold speed. It can be vacuum operated or electric, and the computer controls it and monitors its circuit.

The computer watches the control circuit from its own driver transistor. The P0594 code means an open circuit: the component does not receive current when it is commanded on. Before you replace the part, check the fuse, relay, connector and wiring, which are the most usual cause.

If the servo fails, cruise control shuts off. Check that the throttle cable is not snagged or out of adjustment.

Measure the resistance of the component at its connector. If it is infinite, it is open inside. If it is correct, follow the control wire to the computer looking for a break, especially in the sections near the exhaust or at intermediate connectors.

P0594 code symptoms

  • Check engine light or another warning light on.
  • Cruise control that does not work.

Likely causes of the P0594 code

  1. Connector unplugged or with a broken lock.
  2. Open coil with infinite resistance.
  3. Cut wire. Check the areas where the harness rubs.
  4. Blown fuse, often from an earlier short.

How to diagnose the P0594 code step by step

  1. Activate the component with the scan tool and check whether it responds.
  2. Check the fuse and relay. Measure voltage on both sides of the fuse and swap the relay with an identical one.
  3. Measure the supply at the connector. You should see battery voltage with the key on or when you command it.
  4. Measure the component resistance and compare it with the manual, and also check the insulation to ground.
  5. Check the control wire for continuity to the computer and for the absence of shorts.

How to fix the P0594 code

  • Repair the connector, the wiring or the power supply.
  • Replace the cruise control servo if it does not respond with correct power and command.
  • Clear the codes and verify.

Technical reference data

  • Electric or vacuum servo, depending on the vehicle.
  • Reference values only: check the manufacturer data for your vehicle.

Brand-specific notes

This is uncommon on modern vehicles, where the electronic throttle does this job.

Frequently asked questions about P0594

Can I drive with the P0594 code?
Yes, with caution. The vehicle drives normally, but cruise control will not work until the servo circuit is repaired.
What does the cruise control servo do?
The cruise control servo moves the throttle to hold speed. It can be vacuum operated or electric, and the computer controls it and monitors its circuit.
Does the part always have to be replaced?
No. Check the fuses, relays, connectors and wiring first. They are the most usual cause.
How much does it cost to fix P0594?
As a guide, between $50 and $400.
What does the P0594 code mean?
The P0594 code is a generic OBD2 code for an open circuit in the cruise control servo control circuit. The servo is not getting current when the computer turns it on.

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