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P0585Cruise Control Multi-Function Input "A"/"B" Correlation

The two redundant cruise control switch input signals, Multi-Function Input A and Input B, disagree with each other, so the module cannot trust the driver's cruise commands and disables the system.

Definition

Many cruise control designs feed the steering-wheel switch commands to the module on two separate multiplexed inputs so each button press can be cross-checked. The module continuously compares Input A against Input B, and P0585 sets when the two signals report different button states or fail to track each other within the allowed window. When the correlation fault is present the module ignores cruise commands, so cruise will not set or resume, but the fault has no effect on engine operation. This code points to the switch, clockspring, or wiring rather than the servo or actuator side of the system.

Common causes

  • Worn or internally faulted steering-wheel cruise control switch pod
  • Damaged clockspring (spiral cable) circuit for one of the two switch signals
  • Corroded or spread terminal in the steering column or switch connector
  • Liquid spilled into the switch causing an erratic resistance on one ladder circuit
  • Chafed wiring on one input circuit inside the column harness
  • Control module input circuit fault (least common)

Common misdiagnoses

  • Clockspring replaced when only the switch pod resistor ladder has failed (or vice versa)
  • Brake pedal switch replaced because cruise will not engage
  • Cruise servo or actuator replaced for what is purely an input-side fault
  • Control module replaced before the two switch signal voltages are actually compared

Troubleshooting steps

  1. 1.Compare both inputs on the scan tool

    Watch the Multi-Function Input A and B data PIDs while pressing each cruise button; both should change to the matching state simultaneously, and the one that misbehaves identifies the faulty circuit.

  2. 2.Test the switch resistor ladder

    Disconnect the switch and measure resistance across it for each button press, comparing every step to the service-data chart; an out-of-range or unstable step condemns the switch.

  3. 3.Check the clockspring circuits

    With the wheel turned lock to lock slowly, verify continuity through the clockspring on both signal circuits; a reading that drops out mid-travel means a broken spiral cable.

  4. 4.Inspect column connectors

    Look for corrosion, spread terminals, and evidence of spilled drinks at the switch and base-of-column connectors.

  5. 5.Verify the repair

    Clear the code and operate every cruise button through a full drive cycle, confirming the correlation code does not reset.

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