P0594 Cruise Control Servo Control Circuit /Open
OBD-II Trouble Code Technical Description
Cruise Control Servo Control Circuit /Open
What does that mean?
This is a generic powertrain diagnostic trouble code (DTC) and typically applies to OBD-II vehicles with cruise control. Vehicle makes may include but aren't limited to Dodge, Chrysler, Ram, Jeep, Hyundai, BMW, Vauxhall, Mini, Chevrolet, etc.
There are many benefits that come along with the cruise control feature. On long trips, you do not have to consistently monitor and adjust speeds according to traffic and traffic laws. You press a button or two, and a combination of sensors, solenoids, modules, etc. make sure to keep the vehicle moving at the specified speed until you or possibly outside influences, deactivate or adjust the speed accordingly. Not to mention, the vehicle will have a good idea on how to keep the fuel economy at a good level throughout the trip because well, when we drive we don't necessarily factor everything we could to keep costs down.
Luckily for us, the ECM (engine control module) is responsible for the seamless yet efficient operation of the cruise control. The proper functioning of the systems relies on many sensors, switches, modules, VSS, etc. One of them being the cruise control servo. Most times, these are responsible for controlling the throttle when you set and/or adjust the cruise control. By controlling the throttle and adjusting accordingly, with this servo, the ECM can adjust the speed easily and efficiently. Many times, these servos are controlled mechanically via vacuum lines and throttle cables. The vacuum to the servo is controlled by solenoids who are in turn, controlled by the ECM, who can interpret every other value before specifying throttle position, speed, etc. This fault refers to the circuit involved, refer to the service manual to determine exactly what physical circuit you are working with/ diagnosing.
The P0594 Cruise Control Servo Control Circuit /Open and related codes (P0525, P0595 and P0596) are set when the ECM monitors a malfunction within the cruise control servo control circuit. In the case of the P0594 specifically, it is set when a general malfuction or open electrical condition is detected in said circuit.
Example of a cruise control servo:
What is the severity of this DTC?
I am going to set the severity for this code to medium. As far as most cruise control OBD2 fault codes go, they are fairly minor. That being said, in this case, because the cruise control servo is not only directly connected to the throttle control via cable but is responsible for throttle position at times, it would be more severe than most.
To stress a point, if you neglect any active OBD2 fault, you run the risk of not being aware of any new fault codes. Even when symptomless, if left unattended, OBD2 fault codes can lead to more serious and expensive problems.
What are some of the symptoms of the code?
Symptoms of a P0594 diagnostic code may include:
Cruise control inoperative Erratic cruise control operation Vehicle speed stuck Vehicle speed limited with cruise control active Inaccurate vehicle speed setting when compared to desired or set speed Specific cruise control(s) functions malfunctioning/erraticWhat are some of the common causes of the code?
Causes for this P0594 cruise control code may include:
Defective/damaged cruise control servo Cruise control servo cable broken/stuck/disconnected/mis-adjusted Wiring issue ECM (engine control module) issue Module water intrusion Connector issueWhat are some P0594 diagnostic and troubleshooting steps?
The first step in the troubleshooting process for any malfunction is to research the Technical Service Bulletins (TSB) for known issues with the specific vehicle.
Advanced diagnostic steps become very vehicle specific and may requ
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