Cruise control is very convenient, especially on long trips. The feature allows you to maintain a constant speed and reduces the fatigue that comes from driving. So naturally, if your cruise control stops working, you’ll want to figure out why and fix the problem as soon as possible.
How Does Cruise Control Work?
Before you can begin troubleshooting your car’s cruise control, you need to have a basic understanding of how the system works. There are three primary types of cruise control systems—electronic (with mechanical throttle linkage), electronic throttle, and adaptive—each of which operates a little differently.
Electronic Cruise Control with Mechanical Throttle Linkage
Although each electronic cruise control system is a bit different, a typical setup relies on an electronic actuator and cruise control module. In some systems, the electronic actuator operates a vacuum diaphragm that moves the throttle blade. In other instances, the actuator motor operates the throttle via a cable (without a diaphragm).
When the driver turns on and sets the cruise control, a signal is sent to the control module. The module then activates the electronic actuator, which operates the throttle linkage to move the throttle blade. Modulating the throttle allows the system to maintain engine speed to set a constant vehicle speed.
The control module monitors the vehicle speed sensor (VSS) signal when setting and maintaining the cruise control speed. If the driver applies the brakes (or the clutch pedal if the vehicle has a manual transmission), the brake switch (or clutch switch) sends a signal to the control module, causing the module to disengage the cruise control. The driver can also press the disengage button to deactivate the system.
Electronic Throttle Cruise Control
Electronic throttle cruise control systems do not have mechanical throttle linkage. Instead, the throttle body has an integrated actuator motor that is used to open and close the throttle blade.
In a typical electronic throttle control (ETC) cruise control system, a signal is sent to the body control module (BCM) when the driver activates the cruise control. From there, the BCM passes the signal to the vehicle’s engine computer (often referred to as the powertrain control module). The powertrain control module (PCM) then operates the actuator motor to move the throttle blade and maintain the desired engine speed.
The PCM looks at a variety of sensors and switches while governing the cruise control system. Not only does the module look at signals from the brake switch, VSS, etc., but also the accelerator pedal position (APP) sensors and transmission control module. In addition, depending on the system design, the PCM may also look at signals from the antilock brake (ABS) module and other devices.
Adaptive Cruise Control
Finally, there is a newer type of system, called adaptive cruise control (ACC), that can automatically adjust vehicle speed to maintain a set distance from the vehicle ahead. ACC systems use radar, lasers, cameras, or a combination of the three technologies to detect the leading vehicle.
Information from the radar and/or other sensing devices is shared amongst a variety of control modules on the car’s data network. The modules work together to automatically control the electric throttle, electronic steering, and brake system to make the adaptive cruise control work.
Why is My Cruise Control Not Working? 5 Common Causes
Unfortunately, there isn’t a one-size-fits-all answer to why your car’s cruise control stopped working. There are a variety of cruise control designs used in different vehicles, each of which requires a unique diagnostic approach.
To find out why your car’s cruise control isn’t working, you (or your mechanic) will need to do some troubleshooting. It’s important to consult a repair manual or repair database to determine the correct diagnostic process for your application.
Usually, you’ll find one of the following issues to be the underlying cause of the inoperative cruise control.
Improper Operating Conditions
Before you assume that there’s something wrong with your car’s cruise control, you’ll want to make sure that you’re using the feature properly. Most systems will not engage below a certain speed (usually 25 or 30 mph). Some systems also won’t turn on when the vehicle is traveling above a predetermined speed. Consult your owner’s manual for the cruise control operating instructions for your application.
Sensor and Switch Issues
A problem with the brake switch (or clutch switch), cruise control switch, or VSS can cause issues in any system. More advanced cruise control systems have additional sensing devices (e.g., APP sensors), that can also cause problems.
Control Module Issues
Some vehicles rely solely on a dedicated module to govern the cruise control system. In other instances, many different modules work together to ensure the system is operating as it should.
Regardless of the system design, a problem with one or more of the modules can prevent the cruise control from operating properly.
Wiring and Circuit Problems
Circuit problems, ranging from damaged wiring to a blown cruise control fuse, can prevent the system from working properly.
Faulty Throttle Actuator
On older vehicles, an electric actuator is often used to operate the throttle linkage to maintain the desired cruise control speed. Most late-model vehicles, on the other hand, use an actuator motor to operate the throttle directly. In either scenario, a problem with the throttle actuator can result in inoperative cruise control.
How to Fix Cruise Control
To fix your car’s cruise control system, you (or your mechanic) will need to consult a repair manual or repair database to determine the correct cruise control troubleshooting process. There are many different cruise control systems in use today, and you could end up wasting time and money without the proper repair information.
How Much Should it Cost to Fix Cruise Control?
Exactly how much it will cost to repair your car’s cruise control will depend on what’s wrong with the system. The fix could be anything from a relatively inexpensive brake switch to a costly control module.
What’s more, additional factors, such as the year, make, and model of your vehicle, will influence the cost of the repair.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.