P0585 Cruise Control Multi-Function Input A/B Correlation

Description and meaning of DTC p0585

This generic powertrain diagnostic trouble code (DTC) typically applies to many OBD-II vehicles. That may include but is not limited to vehicles from Dodge, Jeep, Chrysler Ram, Ford, Chevy, Chevrolet, etc. When a code P0585 is stored, it means that the powertrain control module has detected a discrepancy between correlating voltage inputs of the cruise control multi-function switch. Input A/B (or A and B) references a specific but separate set of input circuits. Consult a reliable source of vehicle information to determine exactly which circuits are indicated with this code. The cruise control (or speed control) system is controlled by the PCM, using inputs from the multi-function switch. The multi-function switch is so called because it controls functions in multiple systems. For instance, it may provide input signals for the cruise control system, the turn signals, and the windshield wiper system. Typically, it only acts as a lever for the turn signals but may also house the actual turn signal switch. The driver provides manual inputs using the multi-function switch. These input signals are forwarded to the PCM, which applies the appropriate voltage signal to a cruise control servo motor. These inputs include a command to maintain current vehicle speed, resume a previously maintained vehicle speed, accelerate to increase vehicle speed, or disengage acceleration in order to coast and decrease vehicle speed. Of course, depressing the brake pedal should disengage the cruise control system. Cruise control systems do not generally become active until vehicle speed exceeds 35 mph. The PCM adjusts cruise control servo motor voltage to achieve the appropriate throttle position for maintaining the desired vehicle speed. If the PCM detects an input voltage signal that is not within programmed specifications, or if the vehicle speed cannot be maintained using the cruise control system, a code P0585 will be stored and a malfunction indicator lamp (MIL) may be illuminated. Multiple drive cycles with a failure may be required for MIL illumination.

p0585 diagnostic trouble code symptoms

Symptoms of a P0585 trouble code may include:Inoperative cruise control systemErratic speedometer/odometer operationFlashing or unresponsive cruise control indicator lampOther stored codes

DTC p0585 - possible causes

Causes for this code may include:Defective multi-function switchBad cruise control servo motorOpen or shorted circuits in the cruise control systemFaulty cruise control module, PCM, or programming error

How to fix OBD-II diagnostic trouble code p0585

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. A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle information will be required to diagnose a code P0585. After a visual inspection of 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 prove useful as your diagnosis unfolds. 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, you have an intermittent condition and it may need to worsen before a successful diagnosis can be reached. If the code is reset, continue with your diagnosis. Using your source of vehicle information, obtain component testing procedures and specifications, diagnostic flow charts, connector face views, wiring diagrams, and connector pin-out charts. These items will be necessary to diagnose most codes. Search for applicable technical service bulletins (TSB). If you locate an entry which mirrors the vehicle in question, as well as the code/s stored and the symptoms exhibited, it will likely help you to diagnose the P0585. Check voltage (usually comparable to battery voltage) and ground circuits at the multi-function switch using the DVOM. If no voltage is discovered, use the positive test lead of the DVOM to probe system fuses while grounding the negative test lead to a chassis ground. Fuses should be tested with the circuit loaded to avoid a false result. If there is no ground, you may create a new one for testing purposes, then locate the appropriate ground junction to make sure it is secure. If voltage and ground are both present, use the DVOM to test the multi-function switch following manufacturer’s testing recommendations. Disconnect the switch before testing with the DVOM. If the switch fails to comply with manufacturer’s specifications, consider it defective. If the multi-function switch seems to be functioning properly, use the DVOM to test the cruise control servo motor. Again, follow manufacturer’s recommendations and suspect the motor is defective if it fails to 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. Others use a cruise control system which is integrated with the body control module (BCM) or general electrical module (GEM). If the multi-function switch and servo motor both test appropriately, disconnect the connector from each and use the DVOM to check continuity and resistance on the individual circuits. Circuits which fail to comply with manufacturer’s specifications will need to be repaired or replaced. Don’t be a parts changer. Never automatically condemn the multi-function switch because of this code. Exhaust the diagnostic process before blindly changing parts.

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