Hobbies Cars & Motorcycles Cruise Control Not Working? 9 Potential Causes Share PINTEREST Email Print If your car has cruise control, it can reduce stress and help you stay alert on long drives. gabrieletamborrelli / Getty Images Cars & Motorcycles Cars How Tos Basics Reviews Classic Cars Corvettes Mustangs Tires & Wheels Motorcycles Used Cars Trucks ATVs & Off Road Public Transportation By Benjamin Jerew Benjamin Jerew Benjamin Jerew is an ASE-certified Master Automobile Technician with over a decade of experience in auto repair, maintenance, and diagnosis. Learn about our Editorial Process Published on 08/31/18 Cruise control reduces stress and fatigue on long drives, but if the system isn't working properly, it can become dangerous. If your vehicle's cruise control isn't working, one of the following nine issues may be the root cause. How Cruise Control Works Cruise control is a system to maintain vehicle speed without direct driver input. When you want to engage cruise control, you first turn the system “On” with a button or switch. However, this alone does not start the cruise control. When you “Set” cruising speed, the cruise control module (CCM) records the current speed, then takes control of the throttle body to maintain vehicle speed. When vehicle speed increases or decreases (due to wind or hills, for example), the CCM decreases or increases throttle body opening accordingly. By modulating engine speed, the CCM can maintain your desired cruising speed on the highway. You can increase or decrease cruise speed by tapping a button or lever, and you can cancel cruise control by hitting the “Cancel” or “Off” buttons or stepping on the brake. This electronically-controlled throttle body is modulated directly by the engine control module, both for direct driver input and cruise control. Marin Tomas / Getty Images Throttle body control has changed over the years. Early systems used a vacuum motor and cable, but these eventually changed over to electric motors. Most recently, with the development of drive-by-wire or electronic throttle control systems (ETCS), cruise control is built into the engine control module (ECM), which controls the throttle body electronically. Basic cruise control systems still require the driver to pay attention to changing road and traffic conditions. Adaptive cruise control systems, sometimes called "smart" cruise, use radar or laser detection to maintain safe distances from vehicles ahead. Some adaptive cruise control systems merely reduce engine speed to maintain distance, but some of the newest adaptive cruise control systems can also engage the brakes to slow or stop the vehicle. Still, even with adaptive cruise control, it's important that drivers never take their eyes off the road. Why Is My Cruise Control Not Working? There are a few basic ways that cruise control can fail, depending on how the system is designed. You may not be able to do much about ETCS cruise control systems, but there are a few things you can check: Brake Light Switch – As cruise control is automatically cancelled by depressing the brake, some vehicles may disengage cruise control if it cannot detect the brake light switch. Brake Lights – In some systems, cruise control is disabled when a brake light is blown. Aftermarket lighting, such as LED brake light conversion, might trick the CCM into thinking a brake light is blown, as LED bulbs draw less current than incandescent bulbs. Fuses and Relays – On some vehicles, fuses and relays are used to protect the cruise control actuator circuit. If the fuse is blown or the relay is faulty, the system won’t work. Spiral Cable – Many vehicles mount the cruise control switch on the steering wheel. A faulty spiral cable may have an open circuit, preventing the switch from contacting the CCM. Control Switch – If the internal contacts wear out, the cruise control switch may not be able to contact the CCM. This might disable cruise control completely, or it might not react to the cancel or accelerate functions. Check Engine Light – On some modern vehicles, particularly those equipped with ETCS, cruise control may be disabled if there is an engine or transmission problem. Vacuum leaks on this older cruise control actuator may prevent it from working. Hans Haase / Wikimedia Commons Vacuum Leak – Some older vehicles used vacuum actuators to control the throttle body during cruise control operation. If there is a leak, such as a cracked hose or tube, the system won’t work. A vacuum leak might cause the engine to idler higher or set a fuel trim code. Vehicle Speed Sensor – There are usually multiple vehicle speed sensors (VSS) on any given vehicle. The CCM might use a VSS feed from the ECM, instrument cluster, or transmission. If that signal is lost, the CCM can’t detect vehicle speed, disabling cruise control. Electrical Problems – As most cruise control systems use electrical or electronic components, any diagnosis should include a thorough check of source voltage, wiring harnesses, and connectors. Anything loose or broken could disable the system entirely. If your cruise control isn’t working properly, avoid using it until it is repaired. A faulty cruise control system may not cancel on demand, which will create a safety hazard for you and those around you. After assessing your cruise control yourself, take your vehicle to a trusted mechanic for a check or a couple diagnosis and repair.