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DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P0585

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

P0585 means the cruise control module is receiving conflicting signals from the multi-function switch inputs 'A' and 'B', which should always agree on the requested cruise function. The computer compares these two redundant inputs and sets the code when their voltages or logic states do not correlate as expected, indicating a wiring fault, switch failure, or module issue.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • Cruise control does not engage or drops out unexpectedly while driving
  • Cruise control indicator light flashes or stays off when the button is pressed
  • Steering wheel buttons for cruise control feel unresponsive or require extra force
  • Other steering wheel-mounted controls (horn, audio) may also act erratically if the clock spring is involved
  • Often no symptoms besides the warning light, with cruise still working intermittently

Common causes, most likely first

  1. Faulty multi-function switch or cruise control button assembly on the steering wheel
  2. Damaged or worn clock spring (spiral cable) in the steering column causing intermittent signal loss
  3. Corroded, loose, or chafed wiring between the switch and the cruise control module
  4. Failed cruise control module or body control module not processing the redundant inputs correctly
  5. Poor ground connection at the switch or module, leading to voltage reference drift
  6. Aftermarket steering wheel or radio installation disturbing the switch wiring

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, and record freeze-frame data to see which input was out of range
  2. Inspect the steering wheel switches and clock spring for visible damage, corrosion, or loose connectors
  3. Measure resistance and voltage on both 'A' and 'B' signal circuits at the switch and at the module, comparing to factory specifications
  4. Perform a wiggle test on the wiring harness and clock spring while monitoring live data for the cruise inputs
  5. Check and clean all grounds related to the cruise control system and steering column
  6. Replace the multi-function switch or clock spring if resistance values are out of spec or signals drop intermittently
  7. If all inputs and wiring test good, substitute a known-good cruise control module or reprogram the existing module as a last step

Why redundant inputs disagree on this code

  • The 'A' and 'B' inputs are deliberately redundant, so a single stuck button or shorted wire can make them disagree even when cruise still works most of the time.
  • A worn clock spring often causes P0585 before any airbag or horn symptoms appear, because the cruise circuits are the first to lose contact as the spiral cable flexes.
  • Aftermarket steering wheel covers or phone mounts that pinch the column wiring can set this code intermittently, which is easy to overlook during diagnosis.
  • Some vehicles set P0585 when battery voltage is low during cranking, so always clear the code and verify it returns before replacing parts.
  • The code can be stored by a module that is not the cruise control module itself, so check all modules on the network for related communication or voltage codes.

Can I keep driving with P0585?

The vehicle remains safe to drive because cruise control is a convenience feature and the fault does not affect braking, steering, or throttle response. Avoid using cruise control until the fault is repaired, especially in traffic or bad weather, and address the issue promptly if the horn or airbag warning light also appears.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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