Faulty cruise control switch or stalk (worn contacts or internal fault); Wiring damage, chafing or corrosion in the switch circuits, including between the steering column and the control unit; Poor connection or contamination at the switch or control unit connector; Faulty brake pedal switch or clutch switch giving a conflicting cancel signal, depending on the model; Damaged clock spring or steering column wiring on vehicles where the switch is on the steering wheel; Fault in the control unit or the module that reads the switch signals; Outdated control unit software where the manufacturer has issued a correction for this code.

P0585

Cruise Control Multi-Function Input A/B Correlation.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
85: FaultThe specific fault in that area

What it means

P0585 means the control unit has compared the two signals from the cruise control multi-function switch (inputs A and B) and found they do not agree with each other. The two circuits are meant to give matching or logically related readings, so a mismatch suggests a fault in the switch, its wiring or the module reading it. The exact switch layout and where it is mounted vary by vehicle.

Symptoms

Cruise control will not set, resume or hold speed
Cruise control cancels itself unexpectedly
Cruise control indicator light flashing or not lighting
Engine management light on
Steering wheel or stalk cruise buttons intermittent or unresponsive
Brake light or brake switch related faults stored alongside

Possible causes

Faulty cruise control switch or stalk (worn contacts or internal fault)likely
Wiring damage, chafing or corrosion in the switch circuits, including between the steering column and the control unitlikely
Poor connection or contamination at the switch or control unit connectorpossible
Faulty brake pedal switch or clutch switch giving a conflicting cancel signal, depending on the modelpossible
Damaged clock spring or steering column wiring on vehicles where the switch is on the steering wheelpossible
Fault in the control unit or the module that reads the switch signalsrare
Outdated control unit software where the manufacturer has issued a correction for this coderare

How to diagnose

Read all stored codes and freeze frame data, and note any brake switch, clutch switch or other cruise related faults
Check the cruise control operation and note which buttons work and which do not
Inspect the switch, steering column area and visible wiring for damage, chafing, water ingress or corrosion
Check the connectors at the switch and control unit for tightness, bent pins and green or white corrosion
View live data for the cruise switch inputs and operate each button, checking that both signals change as the manufacturer specifies
Check the brake and clutch switch operation and their signals in live data
Test switch circuit resistance, voltage and continuity against the manufacturer's data, wiggling the wiring to find intermittent faults
Check for relevant software updates or technical bulletins for the model before condemning the control unit

How to fix

Replace the cruise control switch or stalk if it fails testing
Repair or replace damaged wiring and terminals in the switch circuits
Clean, reseat or replace corroded or loose connectors
Replace a faulty brake or clutch switch and check its adjustment
Replace a faulty clock spring or column wiring where fitted
Update the control unit software if a known fault applies, or replace the module only after all else is proven good

Can I keep driving?

Low severity

The car is normally safe to drive without cruise control, so it can be booked in at your convenience. Check that the brake lights work correctly, as a faulty brake switch can also be involved.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.