Cruise Control Multi-Function Input "A" Circuit Range/Performance
Diagnostic trouble code P0579 indicates that the Powertrain Control Module (PCM) has detected an irrational or out-of-range voltage signal from the cruise control multi-function switch circuit 'A'. The engine computer sets this code when the resistance or voltage values from the steering wheel cruise control buttons do not match the expected parameters for a given command.
This code primarily affects the cruise control system and does not impact the vehicle's core drivability or safety. It is safe to drive the vehicle, though the cruise control feature will likely be disabled until repaired.
Common symptoms
- Check engine light illuminated
- Cruise control system is completely inoperative
- Cruise control indicator light fails to turn on
- Inability to set or maintain a specific cruising speed
- Cruise control unexpectedly disengages while driving
Likely causes
- Faulty cruise control multi-function switch (buttons on steering wheel)
- Damaged or failing steering wheel clock spring
- Liquid damage or debris inside the cruise control switch assembly
- Corroded, damaged, or loose wiring connections in the steering column
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Verify the code and check for other related steering column codes.
Look for: If clock spring codes or airbag codes are also present alongside P0579, the clock spring is highly suspect and should be prioritized.
Visually inspect the cruise control buttons for physical damage, sticking, or signs of liquid spills.
Look for: Buttons that do not click properly, stick when pressed, or have sticky residue indicate a mechanically failed switch assembly.
Use a scan tool to monitor the cruise control switch PID data while pressing the buttons.
Look for: The scan tool should show the correct button state (e.g., SET, RESUME, CANCEL). If the state reads 'Invalid' or doesn't change when pressed, the switch or circuit is faulty.
Test the cruise control switch resistance with a digital multimeter.
Look for: Compare the resistance values of each button press to the manufacturer's specifications. Out-of-spec resistance confirms a bad switch.
Test the clock spring continuity while slowly turning the steering wheel.
Look for: If continuity drops out or resistance spikes while turning the wheel, the clock spring ribbon cable is broken and requires replacement.
This page explains the generic P0579 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.