The ‘Adaptive Cruise Control Unavailable’ warning is an indication that the system has been disabled. The issue is often because of an obstructed camera lens or objects detecting sensors. A blown fuse, faulty brake module or speed sensor can also trigger the warning.
Adaptive cruise control is an advanced driver-assistance system introduced by Mitsubishi in 1992. Since then, other automakers have designed the same system, calling it different names. From adaptive cruise to smart cruise, active cruise, dynamic cruise, the list goes on.
Regardless of whatever the system is called, they all perform the same function. Regulate the vehicle’s speed to maintain a safe following distance from other vehicles. The system relies on several sensors and other components to detect objects.
Whenever the system is activated, it communicates with the ECU. The ECU, in turn, communicates with the appropriate components to regulate the vehicle’s speed. The system has been refined over the years, creating smarter adaptive cruise systems.
But any issue with one of the components of the adaptive cruise system will prevent it from engaging. Anytime the system detects an issue, it triggers the ‘Adaptive Cruise Control Unavailable’ warning to notify the driver.
An issue with the object-detecting sensor
Vehicle manufacturers use varying types of sensors for their adaptive cruise control systems. These sensors perform the same function — detect objects on the road. And the most common sensors are Radar and Laser-based systems.
Any issue with the sensor will prevent the sensor from detecting the objects ahead. This invariably triggers the failure of the adaptive cruise control. Depending on the vehicle’s make, something as little as a faded lane marker can disable the system.
The vehicle can disable the adaptive cruise control feature because of the following:
- Broken sensor
- Poor sensor visibility due to inclement weather or obstructions on the sensor. Having snow, ice, dust, or mud on the sensor will obstruct the view.
- The vehicle ahead is riding too low or has an irregular shape
Ordinarily, the system would become available once the weather is back to normal. But you may need to clean the sensor to get it back online if an object is obstructing its view. For a broken sensor, the only option is to get a replacement.
Obstructed camera view
The manufacturers sometimes pair the sensors with camera systems for accurate object detection. But it is also not unusual for a vehicle to rely only on the camera for object detection.
Bright sunlight or glare from other light sources can disrupt the camera’s view, disabling adaptive cruise. A broken, dirty or obstructed camera lens will also prevent the system from engaging.
Check that you didn’t block the camera view if you recently repainted or wrapped your car. Clean the camera or remove any object blocking its view. You also want to check that the camera isn’t broken before getting an OBD scanner to read the system for error codes.
The adaptive cruise control can also fail to engage because of a blown fuse or bad relay. All electrical components, including the adaptive cruise control, have a corresponding fuse. The fuse breaks the circuit to prevent the system from voltage overload during a power surge.
Most vehicles have two fuse boxes. One in the engine bay and the other in the glove box or under the driver-side dashboard. The fuse box in the engine bay usually contains the fuse for electronic drive features, like adaptive cruise control.
You should check your owner’s manual for the location of the corresponding fuse. If the wire inside the fuse has melted, you will need to replace the fuse.
Faulty brake module
The system maintains a safe following distance by decreasing the vehicle’s speed when necessary. It does this by working in concert with the brake system. An issue with the brake module can disable the system. And trigger an ‘Adaptive Cruise Control Unavailable’ warning.
A poorly calibrated brake pedal position sensor is often the issue with the brake module. The error makes the system believe that the driver is depressing the brake, prompting it to disengage. In some vehicles, a blown brake bulb can also prevent the system from engaging.
Replacing blown brake bulbs is a great way to start. Then you can proceed to check the brake pedal position sensor readings. If the sensor reads that the pedal is depressed when fully extended, you will have to recalibrate the sensor.
Faulty vehicle speed sensor
The adaptive cruise control relies on the speed sensor to detect the vehicle’s speed. The ECU uses the data from the speed sensor to regulate the speed accordingly. The failure of this sensor will disable the adaptive cruise control as the system can’t detect the speed. This trigger an “Adaptive Cruise Control Unavailable” warning.
A quick web search for your specific vehicle would reveal the location of your speed sensors. Use a multimeter to test the sensor before replacing it to check that the fault was from a bad-speed sensor.
Bad control switch
A non-functional adaptive cruise button can prompt an ‘Adaptive Cruise Control Unavailable’ warning. The button activates the system and is usually located on the steering wheel. The button command is transmitted through a clockspring behind the steering wheel.
The failure of this clockspring hinders the transmission of any command. And since the adaptive cruise button needs the clockspring to relay its commands, the button stops working once it fails.
If your adaptive cruise control button stops working, it is often due to a bad clockspring. The button should start working once you replace the clockspring.
The adaptive cruise control feature helps reduce fatigue when driving long distances. And something as little as a bright light or inclement weather can disable the system.
But most times, its failure is often due to poor sensor visibility or a blown fuse. A faulty brake module, speed sensor, and a bad control switch can also disable the system. The system notifies the driver by displaying the ‘Adaptive Cruise Control Unavailable’ warning.