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P0593 is a diagnostic trouble code (DTC) for "Cruise Control Multi-Function Input “B” Circuit High". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $70.00. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $30.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
The P0593 trouble code signals an error with the cruise control multi-function input “B” circuit.
The P0593 code is a generic OBD-II trouble code that detects an issue with the cruise control multi-function input “B” circuit, with the “B” referring to a certain area of the circuit, rather than one specific component. The multi-function input circuit is an important part of the cruise control system, which is controlled by the cruise control module and the powertrain control module (PCM). These two control modules work in tandem to automatically control the vehicle’s speed. When the PCM notices that the speed can no longer be controlled, the cruise control system will be thoroughly checked. If the PCM notes that the cruise control multi-function input circuit is producing a voltage or resistance level that is not within the standard range, the P0593 code will be triggered.
Far and away the most common cause of the P0593 trouble code comes from a defective cruise control switch, which is usually the result of a liquid spill on the interior of the vehicle. However, it is also possible that there are damaged electrical components in the cruise control system, such as corroded connectors and shorted wires.
If the P0593 code has been detected, the check engine soon Warning Light will likely illuminate on the dashboard, though this doesn’t happen in all vehicles. The cruise control system will almost always be inoperable, and it’s fairly common that some fuses will be blown as a result of the code.
The P0593 code will be diagnosed with the help of a standard OBD-II trouble code scanner. A trustworthy mechanic will use the scanner to view the freeze frame data for the code, and to check for the presences of any other trouble codes. If the mechanic notices that multiple trouble codes are present, they will be diagnosed in the order in which they appear. The codes should then be reset, and the vehicle restarted, to see if the code remains detected. If the code disappears following the reset, then presume an intermittent error or an inaccurate detection.
If the P0593 code remains detected, then the technician will need to visually inspect all of the electrical components associated with the cruise control system. Special attention should be given to fuses, which frequently blow when the code is detected (either as a cause, or as a reaction). If the electrical components are all undamaged and working, then the issue is most likely the cruise control switch, which will require replacement.
If the issue still remains, a more thorough inspection will need to be performed on the vacuum supply system and the PCM.
After any component is replaced, the technician will need to once again reset the trouble codes, restart the car, and check for the presence of the code. By doing this, the mechanic will know as soon as the problem causing the code has been handled.
The most frequently made diagnostic mistake with the P0593 code is the failure to comply with the OBD-II diagnosis protocol. It is essential that mechanics follow the protocol to avoid erroneous repairs, and don’t overlook simple fixes. Failure to do so often results in blown fuses – a very simple fix – being overlooked.
A vehicle with the P0593 trouble code will still be drivable, but the cruise control system will most likely fail to work. This code is not pressing or dangerous, but should still be addressed sooner rather than later.
The P0593 trouble code only applies to vehicles that have cruise control systems.
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