Worn, dirty or faulty cruise control switch or stalk contacts; Damaged clock spring or wiring in the steering column (on wheel-mounted controls); Corroded, loose or contaminated connector terminals in the switch circuit; Wiring fault such as chafing, a short to earth or voltage, or high resistance; Faulty or misadjusted brake or clutch pedal switch giving conflicting signals; Fault within the control unit that reads the switch input; Outdated control unit software where the manufacturer has issued a known fix.

P0579

Cruise Control Multi-Function Input A Circuit Range/Performance.

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
79: FaultThe specific fault in that area

What it means

P0579 is the generic code for a range or performance fault in the cruise control multi-function input 'A' circuit. The control unit monitors the signal from the cruise control switch or switches (set, resume, cancel and so on) and has seen a value that is out of the expected range, implausible, or not consistent with other inputs such as the brake switch. The exact circuit layout, such as resistor-ladder or separate switch lines, depends on the vehicle.

Symptoms

Cruise control will not set, resume or cancel
Cruise control cuts out unexpectedly
Cruise control warning light or message displayed
Stored fault with the engine management light on in some vehicles
Steering wheel or stalk buttons feel worn or respond intermittently

Possible causes

Worn, dirty or faulty cruise control switch or stalk contactslikely
Damaged clock spring or wiring in the steering column (on wheel-mounted controls)likely
Corroded, loose or contaminated connector terminals in the switch circuitpossible
Wiring fault such as chafing, a short to earth or voltage, or high resistancepossible
Faulty or misadjusted brake or clutch pedal switch giving conflicting signalspossible
Fault within the control unit that reads the switch inputrare
Outdated control unit software where the manufacturer has issued a known fixrare

How to diagnose

Read all stored codes and freeze frame data, noting any brake switch, steering or body control codes, then check for related technical service information for the model
Test every cruise control function and note which buttons fail or behave intermittently
Inspect the switch, stalk and visible wiring and connectors for damage, moisture and corrosion
Check the brake pedal switch (and clutch switch if fitted) operation and adjustment, and confirm brake light operation
With a scan tool, watch the live switch input data while pressing each button and compare it with the expected values for that model
Measure the switch circuit resistance and voltage against manufacturer specifications, wiggling the wiring and connectors to look for intermittent faults
Check the clock spring continuity and wiring between the switch and the control unit if the controls are on the steering wheel
Check the supply and earth to the control unit and for any available software update before considering the control unit itself

How to fix

Replace the faulty cruise control switch or stalk assembly
Repair or replace damaged wiring and clean or renew corroded connector terminals
Replace the clock spring if testing shows a fault in the steering wheel circuit
Replace or correctly adjust the brake or clutch pedal switch
Update the control unit software only if a known fault is documented for the vehicle
Repair or replace the control unit only after all other causes have been ruled out

Can I keep driving?

Low severity

The car is generally safe to drive without cruise control, so it can be booked in at your convenience. Make sure 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.