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P0579 OBD-II Trouble Code: Cruise Control Multi-Function Input A Circuit Range/Performance

Check Engine Light

P0579 OBD-II Trouble Code: Cruise Control Multi-Function Input A Circuit Range/Performance

P0579 code definition

The P0579 code signifies that the car’s computer has found a malfunction in the cruise control multi-function input A circuit.

What the P0579 code means

If your car’s computer notes a malfunction in the cruise control multi-function input A circuit, it will set the P0579 code and may turn on the Check Engine light. The multi-function input circuit is really just the control switch for the cruise control system. It allows you to set a speed, resume, accelerate, decelerate and more. However, if it malfunctions, the cruise control system will not be able to be controlled safely, so the computer will turn it off and set a warning code.

What causes the P0579 code?

A couple of different causes may set the P0579 code, including the following:

  • A faulty cruise control switch
  • Damage from liquids spilled on the cruise control switch
  • Damaged wiring
  • An open or short in the cruise control circuit
  • A blown fuse (often a symptom, but sometimes a cause)

What are the symptoms of the P0579 code?

There are very few symptoms associated with the P0579 code. The car’s Check Engine light may or may not come on. The cruise control system will be inoperable until the problem is fixed.

How does a mechanic diagnose the P0579 code?

Diagnosing the P0579 code requires the mechanic to first connect an OBD II scanner to the car’s computer. The codes will be read, noted and then cleared, and the car will be test driven to see if the codes reset. The mechanic should also test the cruise control system for operation during the test drive.

If the codes return and/or the cruise control system remains inoperable, the mechanic should test the cruise multi-function switch for operability. This is the single most common cause of the code. Doing so will require that the vehicle be put on a lift, with an assistant operating the gas pedal and the engine running. The mechanic will use a scanner to test the switch for operation. If it fails the test, the switch should be replaced.

If the switch operates normally, the mechanic should check the wiring and connectors for opens, shorts and other damage, as well as for loose or corroded connections. Any damage should be repaired, or damaged sections replaced.

The mechanic should also check cruise control fuses prior to and after replacing any parts, as blown fuses are often associated with this particular code.

Common mistakes when diagnosing the P0579 code

One common mistake here is not checking for blown fuses prior to replacing components. Often, a blown fuse can mimic symptoms of switch failure, as can issues like loose connections or broken wires.

How serious is the P0579 code?

The P0579 code is not particularly serious and will not prevent your car from being driven. However, until the problem is fixed, your cruise control system will be inoperable, which can be inconvenient and lead to discomfort and fatigue during long drives. Have the problem diagnosed soon.

What repairs can fix the P0579 code?

In most cases, fixing the P0579 code requires replacing a faulty cruise control switch. However, this is just one of several possible causes. Other potential fixes include:

  • Replacing damaged wiring
  • Cleaning or tightening connections
  • Replacing blown fuses

Additional comments for consideration regarding the P0579 code

While the P0579 code isn’t serious enough to affect drivability, the inconvenience can be significant, particularly if you spend a lot of time driving on highways or interstates.

Need help with a P0579 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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