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P0578 – Cruise Control Multi-Function Input A Circuit Stuck (OBD2)

P0578 means "Cruise Control Multi-Function Input A Circuit Stuck". The control unit has detected a fault in the electrical circuit of the cruise control system: the signal or control current is missing or outside the expected window. The code does not say whether the value is too high or too low, so the wiring and the component itself both have to be checked.

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P0578 quick summary

Fault codeP0578
MeaningCruise Control Multi-Function Input A Circuit Stuck
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityLow
Can I drive?Yes. Only cruise control is affected; the car drives normally.
Repair cost€10 – €400

How cruise control is monitored

Cruise control holds a set speed using signals from the steering column switches, brake and clutch switches and the vehicle speed; these codes cover the switch inputs and, on older systems, the servo and vacuum control.

Modern cruise control is part of the engine control unit: the multi-function switch on the steering column sends on, off, set, resume, accelerate and coast requests, and the electronic throttle holds the speed. Older systems used a separate servo with vacuum and vent valves or a cable actuator.

Codes in this group report faults in the individual switch signals, stuck buttons, implausible combinations (A/B correlation), the servo and its vacuum/vent control, and a vehicle speed that is too high for cruise control.

Cruise control faults do not affect how the engine runs, but the system is disabled. Common causes are worn steering column switches, a faulty clock spring, brake or clutch switch problems and wiring faults.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16962 (P0578). Both numbers mean the same fault.

Symptoms of P0578

  • Cruise control does not engage or switches off
  • Buttons do not respond
  • Cruise control indicator flashing
  • Check Engine light on (some vehicles)
  • No effect on normal driving

Most common causes of P0578 (most likely first)

Mechanic's Pro Tip

If cruise control works only intermittently, watch the switch voltage in live data while turning the steering wheel – a failing clock spring shows dropouts at certain angles.

  1. 1.Damaged wire or loose, corroded connector at the cruise control system

    Most likely

    Green or white corrosion, pushed-back pins and chafed insulation near hot or moving parts are the most common findings.

  2. 2.Faulty cruise control system

    An internal break or short in the component itself.

  3. 3.Blown fuse or missing supply voltage

    If several codes appeared at the same time, check the shared fuse, relay or ground point first.

  4. 4.Brake or clutch switch fault

  5. 5.Servo or vacuum/vent valve fault (older systems)

Step-by-step diagnostic guide

  1. 1

    Read codes and switch status

    Read the codes and watch each cruise control switch input in live data while pressing the buttons.

  2. 2

    Check the circuit with a multimeter

    With the ignition off, unplug the cruise control system and the control unit connector (or back-probe), then check each wire between them for continuity and for shorts to ground and to battery voltage. Compare the component's resistance or supply voltage with the value in the repair manual.

    Multimeter: Wire continuity: below about 1 Ω. Wire to ground with both connectors unplugged: no continuity. Supply/reference with ignition on: usually 5 V for sensors, battery voltage for actuators.

  3. 3

    Check brake and clutch switches

    Make sure the brake and clutch switch signals are correct – cruise control will not engage if they report 'pressed'.

  4. 4

    Measure the switch

    Check the switch resistances or voltages per button according to the wiring diagram.

    Multimeter: Many multi-function switches use a resistor ladder: each button gives a different voltage on one signal wire.

  5. 5

    Check the clock spring

    If the switch is on the steering wheel, check the clock spring for open circuits (often other steering wheel functions fail too).

  6. 6

    Replace and verify

    Replace the switch or repair wiring and test cruise control on the road.

Frequently asked questions

Can I keep driving with P0578?

Yes. Only cruise control is affected; the car drives normally.

How much does it cost to fix P0578?

Typical repair costs are 10 € – 400 €, depending on the cause and the vehicle. The most common fixes are: damaged wire or loose, corroded connector at the cruise control system; faulty cruise control system; blown fuse or missing supply voltage. Always confirm the cause with the tests above before buying parts.

Does a cruise control code affect the engine?

No. The engine runs normally; only the cruise function is disabled.

Why does cruise control need the brake switch?

For safety it must disengage when you brake, so a brake switch fault disables it.

What is the difference between P0578 and similar codes?

P0578 belongs to a group of codes for the same component that differ in the type or location of the fault: P0575 – Cruise Control Input Circuit; P0576 – Cruise Control Input Circuit Low; P0577 – Cruise Control Input Circuit High; P0579 – Cruise Control Multi-Function Input A Circuit Range/Performance; P0580 – Cruise Control Multi-Function Input A Circuit Low; P0581 – Cruise Control Multi-Function Input A Circuit High. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.