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Diagnosing Cruise Control Issues

Cruise Control icon

Cruise control has come a long way in the past few decades and has gone from being an expensive luxury item to a common standard piece of equipment in vehicles. Sometimes, though, it stops working or begins fluctuating speed levels. Today, cruise control offers both basic functionality (holding a specific speed without throttle input) to advanced functions to include radar-assisted or camera-based adaptive cruise control.

Basic Functions of Cruise Control

The basic functions of the cruise control system in today's vehicles are an on/off button (used to toggle the system), a "set" button to set desired speed, a "cancel" button to temporarily cancel cruise control and return throttle control to the driver, a "resume" button to return cruising to the already-set speed, and "speed up" or "slow down" buttons to increase or reduce cruise control speed settings.

On most vehicles, the cruise control system is operated using four buttons. One turns the system on and off. Another cancels the current setting. A third and fourth set or decrease speed and resume or increase speed. Some systems swap these functions among the controls, but the way we've listed them is generally standard within the industry now.

Electronic Cruise Control

The most common type on the road today, electronic cruise control maintains speed and controls the throttle entirely with a computer. Older cruise control models used mechanical and quasi-mechanical devices to operate the throttle, usually with a vacuum actuator. Today's vehicles, and those produced in the past two decades, usually use an electronic throttle control rather than mechanical linkage, which eliminated the need for quasi-mechanical cruise control systems and paved the way for fully electronic cruise control.

Inputs from the driver through the steering-mounted or similar control sets program the Body Control Module (BCM) with settings for the cruise control system. It, in turn, will maintain the cruise through inputs and monitoring of the vehicle's speed from information given and transmission to the Power Control Module (PCM, or engine computer). Some systems use the car's internal network bus to do the same.

Common components for a modern cruise control system include:

  • Cruise control switches
  • Cruise control module
  • BCM or bus to PCM
  • Brake pedal cancellation switch
  • Clutch pedal switch (same)
  • Vehicle speed sensor
  • Cruise control indicator lamp(s)

Common Faults in the Cruise Control System

Blown fuses are the most likely reason for cruise control in a modern vehicle to stop working. Any short or electrical overload for any reason can affect the cruise control system. Common causes include the cruise control system being engaged during engine start, which can overload the circuit, or moisture in the PCM or BCM. Use standard short diagnosis to find the fault in the cruise control system if replacing the fuse results in another fault.

Misadjusted brake or clutch pedal switches can also be a problem. Sometimes, the pedal becomes loose enough (usually due to a worn out return spring or joint) to "shake" during driving and shut off cruise control. The switch itself could also be bad, requiring replacement.

Engine codes indicating a faulty speed sensor or PCM could also be the problem.

Another common issue are faulty switches on the driver's controls. Spilled drinks, windows left open during inclement weather, and other causes can gum or short these switches, making them inoperable or unpredictable.

Faulty throttle control actuators can also affect cruise and will often manifest with other problems not related to the cruise control, such as lack of acceleration or improper idle.

As with most repairs, check to be sure your vehicle isn't under recall for its cruise control system. Many manufacturers have recalled faulty systems for various reasons and yours could be one of them.