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P0581Cruise Control Multi-Function Input "A" Circuit High

The multiplexed cruise control switch circuit voltage is above its expected range, usually from an open circuit or short to voltage.

Definition

The module monitors the cruise multi-function input, whose voltage should sit at a defined at-rest level and step down through valid values as buttons are pressed. P0581 sets when the circuit voltage rises above the maximum plausible value, which points to an open circuit — a broken wire, failed clockspring, or disconnected switch — or a short to battery voltage. Cruise control is disabled and will not engage until the circuit is repaired; the code has no effect on engine operation, emissions, or the MIL.

Common causes

  • Open in the switch signal wire or its ground return
  • Failed clockspring with a broken conductor
  • Unplugged, corroded, or backed-out terminal at the switch or module
  • Failed cruise switch with an open resistor network
  • Signal wire shorted to a battery-voltage circuit
  • Faulty module input (rare)

Common misdiagnoses

  • Replacing the cruise switch when the clockspring is the open circuit
  • Replacing the brake light switch
  • Replacing the PCM or body control module for a broken wire
  • Replacing the cruise actuator/servo

Troubleshooting steps

  1. 1.Measure the input voltage at the module

    A signal pegged at reference or battery voltage that never changes with button presses confirms an open or short to voltage.

  2. 2.Check end-to-end continuity

    With connectors unplugged, verify the signal and ground wires each read near 0 ohms end to end; an open isolates the fault to that wire segment.

  3. 3.Test the clockspring while steering

    Measure through the spiral cable as the wheel turns; opens that come and go with wheel position condemn the clockspring.

  4. 4.Ohm the switch assembly

    Confirm each button closes to its specified resistance; open readings in all positions indicate a failed switch or its internal ground.

  5. 5.Confirm the repair

    Verify correct voltage steps for every button, clear the code, and road test to confirm cruise sets and holds speed.

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