Technical Description of OBD-II Trouble Code
Correlation between Cruise Control Multi-Function Input A/B
What does that signify?
This generic powertrain diagnostic trouble code (DTC) is commonly found in many OBD-II vehicles, including those from Dodge, Jeep, Chrysler Ram, Ford, Chevy, Chevrolet, etc.
When code P0585 is stored, it indicates that the powertrain control module has detected a discrepancy between the voltage inputs of the cruise control multi-function switch.
Input A/B (or A and B) refers to a specific set of input circuits that are separate from each other. To determine which circuits are indicated by this code, consult a reliable source of vehicle information.
The PCM controls the cruise control (or speed control) system using inputs from the multi-function switch. This switch controls functions in multiple systems, such as the cruise control system, turn signals, and windshield wiper system. It may also house the actual turn signal switch.
The driver provides manual inputs through the multi-function switch, which are then sent to the PCM. The PCM applies the appropriate voltage signal to a cruise control servo motor based on these inputs. The inputs include commands to maintain current vehicle speed, resume a previously maintained vehicle speed, accelerate to increase vehicle speed, or disengage acceleration to coast and decrease vehicle speed. The cruise control system is disengaged when the brake pedal is depressed. Typically, cruise control systems become active when the vehicle speed exceeds 35 mph.
The PCM adjusts the voltage to the cruise control servo motor in order to achieve the desired throttle position for maintaining the desired vehicle speed.
If the PCM detects an input voltage signal that does not meet the programmed specifications, or if the vehicle speed cannot be maintained using the cruise control system, code P0585 will be stored and the malfunction indicator lamp (MIL) may illuminate. Multiple drive cycles with a failure may be required for the MIL to illuminate.
Cruise control stalk:
What is the severity of this DTC?
Since the P0585 pertains only to the cruise control system, it should not be considered severe.
What are some of the symptoms of the code?
Symptoms of a P0585 trouble code may include:
What are some of the common causes of the code?
Causes for this code may include:
What are some P0585 troubleshooting steps?
If the vehicle in question is equipped with a drive-by-wire throttle control system and related codes are stored, diagnose and repair those before attempting to diagnose the P0585.
If throttle position sensor (TPS) codes are stored, they must also be diagnosed and repaired before diagnosing this code.
To diagnose a code P0585, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle information.
After visually inspecting the cruise control system wiring and connectors, connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. Record this information as it may be useful during the diagnosis. Clear the codes and test drive the vehicle normally until the PCM either enters readiness mode or the P0585 is reset. If the former occurs, there may be an intermittent condition that needs to worsen before a successful diagnosis can be made. If the code is reset, continue with the diagnosis.
Obtain component testing procedures and specifications, diagnostic flow charts, connector face views, wiring diagrams, and connector pin-out charts from a reliable source of vehicle information. These items will be necessary to diagnose most codes.
Search for applicable technical service bulletins (TSB). If you find an entry that matches the vehicle in question, the stored code/s, and the exhibited symptoms, it will likely assist in diagnosing the P0585.
Using the DVOM, check the voltage (usually comparable to battery voltage) and ground circuits at the multi-function switch. If no voltage is found, use the positive test lead of the DVOM to probe system fuses while grounding the negative test lead to a chassis ground.
Test the fuses with the circuit loaded to avoid false results. If there is no ground, create a new one for testing purposes and then locate the appropriate ground junction to ensure it is secure.
If both voltage and ground are present, use the DVOM to test the multi-function switch according to the manufacturer’s testing recommendations. Disconnect the switch before testing with the DVOM. If the switch does not comply with the manufacturer’s specifications, consider it defective.
If the multi-function switch appears to be functioning properly, use the DVOM to test the cruise control servo motor. Again, follow the manufacturer’s recommendations and consider the motor defective if it does not comply.
Before using the DVOM to test individual circuit resistance, disconnect all related controllers to avoid damage. Some vehicles use a dedicated cruise control module in addition to the PCM, while others use a cruise control system integrated with the body control module (BCM) or general electrical module (GEM).
If both the multi-function switch and servo motor test appropriately, disconnect the connector from each and use the DVOM to check continuity and resistance on the individual circuits. Circuits that do not comply with the manufacturer’s specifications will need to be repaired or replaced.
