P0596 OBD-II Trouble Code: Cruise Control Servo Control Circuit High

P0596 code definition

The P0596 diagnostic trouble code is an indication that there is an issue with the cruise control servo control circuit.

Related Trouble Codes:

• P0594 OBD-II Trouble Code: Cruise Control Servo Control Circuit/Open
• P0595 OBD-II Trouble Code: Cruise Control Servo Control Circuit Low

What the P0596 code means

When the cruise control feature is in use, vehicle speed is automatically controlled by the Powertrain Control Module (PCM), the cruise control module, and the servo control unit. The Powertrain Control Module (PCM) receives a signal from the cruise control module as to the desired speed of the vehicle. The servo control unit receives information from the Powertrain Control Module (PCM) and cruise control module as to the required position of the throttle plate. The servo control unit will then open or close the throttle plate to maintain the desired speed of the vehicle. The P0596 diagnostic trouble code is stored when the cruise control module is not sending the proper speed signal to the Powertrain Control Module (PCM) necessary to control vehicle speed and the cruise control servo control unit is giving an abnormal voltage or resistance reading.

What causes the P0596 code?

• Faulty cruise control servo control unit

• Blown fuses

• Faulty cruise control servo control wires that are frayed, broken, or shorted

• Faulty cruise control servo control connectors that are damaged or corroded

• Liquid spilled onto the cruise control switch

What are the symptoms of the P0596 code?

• Check engine light is on (not always applicable)

• Cruise control is not working properly

• Blown fuses

How does a mechanic diagnose the P0596 code?

• Diagnostic trouble codes should be diagnosed in the order that they appear in the powertrain control module (PCM).
• Use an OBD-II scanner to collect all trouble codes that have been stored by the powertrain control module (PCM) as well as freeze frame data.
• Inspect the cruise control servo control wiring for frays, breaks, and shorts. Repair or replace damaged wiring as necessary.
• Inspect the cruise control servo control connectors for damage and corrosion. Repair or replace connectors as necessary.
• Check the cruise control switch for proper operation. Also inspect the cruise control switch wires for damage.
• Clear all diagnostic trouble codes from Powertrain Control Module (PCM) and operate the vehicle to see if the P0596 diagnostic trouble code comes back.
• If the P0596 trouble code comes back, check the fuse for the cruise control system. Repair or replace as necessary.
• Check the cruise control switch for proper operation. Also inspect the cruise control switch wires for damage.
• In vehicles with a vacuum controlled cruise control system, inspect vacuum lines, one-way check valve, engine vacuum, and engine vacuum components for damage.
• Repair or replace vacuum lines and engine components as necessary.
• Inspect the cruise control servo and the throttle cable to the servo for damage. Repair or .replace as necessary.
• Clear all diagnostic trouble codes from Powertrain Control Module (PCM) and operate the vehicle to see if the P0596 diagnostic trouble code comes back.
• If the P0596 trouble codes come back, use a digital volt ohm meter to test cruise control servo control unit and the cruise control switch for proper voltage and continuity.
• If the test results of the cruise control servo control unit do not meet the manufacturer’s predetermined specifications the cruise control servo control unit will need to be replaced.
• If the test results of the cruise control switch do not meet the manufacturer’s predetermined specifications, the cruise control switch will need to be replaced.

Common mistakes when diagnosing the P0596 code

The most common mistake made with this code is overlooking blown fuses. Other components should not be replaced without first inspecting the fuses to ensure they are working properly. When components are replaced unnecessarily, it is a waste of time and money and may not resolve the problem.

How serious is the P0596 code?

A diagnostic trouble code is normally considered serious when it causes driveability issues or a change in performance.When this code is stored in the Powertrain Control Module (PCM), the cruise control system will be disabled. This may be considered an inconvenience, but is not considered serious. The P0596 diagnostic trouble code should however, be diagnosed and repaired as soon as possible.

What repairs can fix the P0596 code?

• Replace cruise control servo control unit

• Replace blown fuses

• Repair or replace cruise control servo control wiring that is frayed, broken, or shorted

• Repair or replace cruise control servo control connectors that are damaged or corroded

• Replace cruise control switch

Additional comments for consideration regarding the P0596 code

Liquid spilled on the cruise control buttons has been known to cause the P0596 diagnostic trouble code. Other common causes are faulty wiring and blown fuses.

Need help with a P0596 code?

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