Faulty or sticking cruise control switch or steering wheel control buttons; Damaged wiring, chafing or short to power or earth in the switch circuit; Corroded, loose or contaminated connector at the switch or control unit; Worn clock spring or steering column contacts on cars where the controls feed through it; Brake or clutch pedal switch fault feeding the same input, depending on model; Fault inside the engine control unit or the module reading the input; Outdated control unit software where a manufacturer bulletin lists it as a known cause.

P0590

Cruise Control Multi-Function Input B Circuit Stuck.

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
90: FaultThe specific fault in that area

What it means

P0590 is the generic code for a stuck fault in the cruise control multi-function input B circuit. The control unit has seen a signal from the cruise control switch or related input that stays in one state, or does not match what the unit expects, for longer than it should. The cruise control is normally disabled while the fault is present. What 'multi-function input B' refers to varies by model and manufacturer, so check the wiring diagram for the vehicle.

Symptoms

Cruise control will not engage or cancels itself
Cruise control warning or indicator light on the dash
Malfunction indicator lamp may be on, depending on the vehicle
Cruise control buttons or stalk feel sticky or unresponsive
Cruise control set or resume behaves erratically

Possible causes

Faulty or sticking cruise control switch or steering wheel control buttonslikely
Damaged wiring, chafing or short to power or earth in the switch circuitlikely
Corroded, loose or contaminated connector at the switch or control unitpossible
Worn clock spring or steering column contacts on cars where the controls feed through itpossible
Brake or clutch pedal switch fault feeding the same input, depending on modelpossible
Fault inside the engine control unit or the module reading the inputrare
Outdated control unit software where a manufacturer bulletin lists it as a known causerare

How to diagnose

Read all stored codes and freeze frame data, then note whether the fault is current or intermittent and whether other cruise, brake or switch codes are present.
Check the cruise control switch visually and operate every button, listening and feeling for sticking, damage or spilled liquid.
Inspect the wiring and connectors from the switch to the control unit for chafing, water ingress, corrosion and pushed-back pins.
Using live data, watch the cruise switch input while pressing each button and check that it changes and returns to rest.
Check the brake and clutch pedal switches for correct operation and adjustment, as they often share cruise control logic.
Using the wiring diagram, test the circuit for correct reference voltage, earth and resistance, and wiggle the harness while monitoring for changes.
Where the controls pass through the steering column, check the clock spring and contacts for wear, following the model-specific procedure.
Check for any manufacturer software updates or bulletins for the vehicle before replacing a control unit.

How to fix

Replace the faulty cruise control switch or steering wheel control assembly.
Repair or replace damaged wiring and fix any short or open circuit found.
Clean, repair or replace corroded or loose connectors and ensure pins are seated and secure.
Replace or adjust a faulty brake or clutch pedal switch.
Replace a worn clock spring if testing confirms it is the cause.
Update the control unit software only if a known fault is documented, or repair or replace the control unit once everything else has been ruled out.

Can I keep driving?

Low severity

The car is normally safe to drive as only the cruise control is affected. Book it in at your convenience, but have the brake light and pedal switch checked promptly if they seem faulty as well.

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