Error Code P0585 is defined as Cruise Control Multi-Function Input A/B Correlation. This means there’s a discrepancy between correlating voltage inputs of the cruise control multi-function switch.
This code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system and cruise control system. It commonly appears among, but not limited to, Chevrolet, Chrysler, Dodge, Ford, Jeep, etc. Specifications on the definition, troubleshooting, and repairs vary from type of powertrain, make and model to another.
The PCM (powertrain control module, also known as ECM or engine control in other vehicle makes) controls the Cruise Control system (also referred as Speed Control) through inputs to the multi-function switch. This switch is also referred to as the controls function in multiple systems. It also provides different functions, such as turn signal, windshield wiper system, etc. Typically, it only works as a lever for the turn signal, but can also have the actual turn signal switch.
The driver provides the input using the multi-function switch. This input is then forwarded to the PCM, which applies the voltage signal to a cruise control servo motor. Inputs include a command to keep current vehicle speed, resume the previously maintained speed, accelerate, or disengage acceleration to coast and decrease vehicle speed. Depressing the brake pedal will disengage the cruise control system. Cruise control system is generally inactive until the vehicle reaches 35 mph.
If the PCM detects that an input voltage signal is outside the specifications provided by the manufacturer, or if the vehicle speed can’t be maintained by the Cruise Control system, then Error Code P0585 will be set. For some vehicles, multiple drive cycles may be necessary for the Check Engine light to activate.
This code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:
- Erratic operation of speedometer/odometer
- Inoperative cruise control function
- Flashing or unresponsive cruise control indicator lamp
- Other related error codes may be stored
Defective multi-function switch is the most common cause for this code. Other possible causes include:
- Defective cruise control servo motor
- Open or shorted circuits in cruise control system
- Defective cruise control module
- Damaged or programming error in PCM (rare)
How to Check
If the vehicle comes with a drive-by-wire throttle control system, and related codes are stored, it’s important to diagnose and repair other codes before addressing P0585.
If TPS (Throttle Position Sensor) codes are stored, then they must also be diagnosed and repaired first.
To get more information about the code, use the diagnostic scanner and DVOM (digital volt/ohm meter).
Next, check the cruise control system’s connectors and wirings; connect the scanner to the diagnostic port and then retrieve all stored codes, including the freeze frame data. Record this information, clear the codes, and then take the vehicle to a test drive and see if the code comes back.
If the code does NOT come back, then the problem is intermittent and may have to develop more before you can successfully diagnose it. If the code DOES come back, then continue with the diagnosis.
Refer to your vehicle information for the testing procedures, specifications, flowcharts, wiring diagrams, connector pin-out charts, and connector face views. They’re all necessary for the diagnosis.
Look for the applicable TSB (Technical Service Bulletin) for the code. If you find an entry that reflects the problem with your vehicle, including the symptoms, then that’s likely your diagnosis for the code.
Use the DVOM to check the voltage (generally the same with battery voltage) and ground circuits at the multi-function switch. If there are is voltage detected, then probe the system fuse using positive test lead of DVOM, while grounding the negative test lead to chassis ground.
To avoid a false result, fuses must be checked with the circuit loaded. If there’s no ground, you can make a new one for testing purposes, then find the right ground junction to make sure it’s secure.
If both voltage and ground testing are present, use the DVOM to test the multi-function switch. Follow the recommendations set by the manufacturer. Make sure you disconnect the switch before testing with the DVOM. If the switch fails to comply with the specs set by the manufacturer, then it’s defective.
If the multi-function is in the right condition, use the DVOM to test the cruise control servo motor. Again, check with the manufacturer recommendations. If it fails to comply, that means the motor is defective.
Before using the DVOM for the individual circuit resistance, make sure to disconnect all related controllers to avoid damage. Some vehicles have a dedicated cruise control module in addition to the PCM. Others use a Cruise Control system integrated with the BCM (Body Control Module) or GEM (General Electrical Module).
If the multi-function switch and servo motor look good, disconnect the connector from each and then check for continuity and resistance on the individual circuits using the DVOM. Circuits which fail to comply with the specs set by the manufacturer must be repaired or replaced.
How to Fix
Depending on the diagnosis, common repairs for this code include:
- Replacement of multi-function switch
- Replacement of cruise control servo motor
- Replacement of damaged connector circuits
Never be a parts changer or automatically condemn the multi-function switch for this code. Make sure you exhaust the diagnostic process changing any parts.