What it means
Cruise control uses two redundant multiplexed inputs (A and B) for safety. The two inputs do not agree - one reports a button press the other does not, or both report incompatible levels at the same time.
At a glance
- Usually lights the check-engine light
How it works
The cruise-control module compares two redundant multi-function inputs, A and B, to verify that the switch commands agree. P0585 sets when the two inputs report incompatible states, such as one indicating a button press while the other does not.
Common causes
Most likely first.
- Faulty cruise-control switch or stalk
- Damaged or corroded wiring or connectors
- Poor electrical connection
- Fault in the cruise-control module
Symptoms
- Cruise-control buttons may work inconsistently
- Cruise control may be unavailable or disengage
- Check-engine light
How to diagnose it
- Review freeze-frame and scan-tool data for both A and B inputs while the controls are released and as each cruise button is pressed.
- Inspect the switch or stalk and its connectors for looseness, corrosion, damaged pins, or moisture that could affect one input differently.
- Operate each button while watching both input states to identify a command that is missing, erratic, or inconsistent between A and B.
- Check the A and B signal wires separately for opens, shorts, and poor terminal contact using the wiring diagram.
- If both circuits and the switch produce matching signals at the module connector but scan data still disagrees, test the cruise-control module per the manufacturer's procedure.
Common fixes
- Clean and secure the cruise-switch connectors and terminals.
- Repair damaged wiring on the A or B input circuit.
- Replace a faulty cruise-control switch or stalk if its redundant outputs disagree.
- Correct poor connections or damaged pins at the module connector.
- Repair or replace the cruise-control module only after verifying both input circuits.
Can I keep driving?
The module may disable cruise control or cancel it if the two inputs disagree. Normal driving is generally possible, but use the accelerator and do not depend on cruise control.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.