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Error Code P0596 is defined as Cruise Control Servo Control Circuit High, meaning there’s an ongoing problem in the cruise control servo control circuit, which is likely caused by blown fuses, broken wires, or the faulty unit itself.
This error code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system. It’s particularly common among certain brands like BMW, Chevrolet, Chrysler, Dodge, Hyundai, Jeep, Ram, Vauxhall, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and/model to another, and powertrain type.
Cruise control system has lots of uses; for long trips, drivers are given the convenience not to have to monitor and adjust speed to traffic and traffic laws consistently. There are buttons(s) and a combination of sensors, modules, solenoids, etc. that will ensure the vehicle is moving at a specific speed for easy and safe driving. This feature helps significantly in terms of fuel economy.
The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) is responsible for the efficient operation of the cruise control system. The proper function of the system relies on many factors, such as switches, sensors, modules, VSS, etc. One of which is the cruise control servo; which is usually responsible for adjusting the throttle when the cruise control is set and adjusted. By controlling the throttle and adjusting accordingly, with this servo, the PCM can adjust the speed easily and efficiently. In many cases, the servo is controlled by the PCM, which can interpret every other value before specifying throttle position, speed, etc.
Error Code P0596 is set when the PCM monitors a malfunction within the cruise control servo control circuit; it specifically means that there’s a high voltage electrical condition detected in the said circuit.
Other related error codes include:
As with other cruise control related error codes, cruise control function is inoperable if this condition is present. Other common symptoms include:
- Erratic cruise control operation
- Stuck vehicle speed
- Vehicle speed limit with cruise control active
- Inaccurate vehicle speed setting (compared to desired or set speed)
- Other functions of cruise control are erratic
The most common cause for this code is failed cruise control servo control unit, as it results to abnormal voltage or resistance levels. This is particularly common in older vehicle models that integrate the servo with cruise control mode.
Other possible causes include:
- Defective cruise control servo control unit
- Faulty wires (broken, frayed, or shorted) in the cruise control servo
- Damaged or corroded cruise control servo connectors
- Liquid spilled on cruise control switch
How to Check
As with most codes, the best thing to do before a diagnosis is to check with the TSB (technical service bulletin) for known issues with the specific vehicle. Some vehicles may require advanced diagnostic steps and special tools, which differs from one type of vehicle to another. Here are some basic steps for diagnosis.
Cruise control servo are usually mounted in the somewhere in the engine compartment. Usually, they’re in close to the throttle body, as they control vehicle speed. After locating the component, check it thoroughly. Pay close attention to the cable and look for any signs of corrosion, fraying, kinks, or any signs or malfunctions. If the servo cable doesn’t freely move when controlling the throttle, the PCM could see it as a problem.
Also, check the physical condition of the servo itself, as it could be a tell-tale sign of a problem. Make sure you check all the vacuum lines that run to the servo. Any cracks or deterioration in the lines should be a tell-tale sign of the state of the vacuum system. Thus, it’s highly recommended to replace vacuum lines. They’re pretty inexpensive and could save you from further problems in the future.
In terms of the electrical, check the connector on the servo. Repair any broken tabs or loose connections. The harness could be running through tight areas and moving parts, so look for any chafing areas that could cause a problem. Repair or replace broken or damaged wires.
The cruise control fuse must also be checked for damage. If problems persist, the cruise control switch and servo solenoid must be tested for continuity before being replaced. In other cases, the servo itself malfunctions and must be replaced.
Depending on the capabilities of your OBD-II scanner, you can monitor the operation of the servo through it while connected to the vehicle. It can display percentage or electrical values. Either way, you can use these values to check the physical operation by watching it under the hood, with wheels off the ground. Note that this is procedure usually applies to older vehicles.
How to Fix
Depending on your diagnosis, common repairs for this code include:
- Replacement of cruise control servo control unit
- Replacement of blown fuses
- Repair or replacement of cruise control servo control wires (broken, frayed, or shorted)
- Repair or replacement of cruise control servo control connector (corroded or damaged)
- Replacement of cruise control switch
Make sure the vehicle’s manufacturer advises any procedure you do in your diagnosis. Thus, make sure you research thoroughly.