Vehicle Speed Sensor Failure
Vehicle speed sensor (VSS) is the eye of the cruise control module, that monitors the speed of the vehicle by sending alternating current signals, whose frequency is directly proportional to speed. When the vehicle speed sensor fails, it can no longer receive signal information about vehicle speed, rendering it blind and useless. VSS failure is one of the most common cruise control problems that you could face. How can you know that cruise control not working is a result of VSS failure? Look at the speedometer, as it is dependent on the VSS too. If the cruise control and speedometer stop working simultaneously, you are facing VSS failure. In such a case, the only way out is to repair or replace the VSS.
Cruise Control Module Problems
The cruise control module is the brain of the cruise control mechanism. It processes the signals it receives from the VSS, compares it with set speed value and prods the actuator to accordingly control the throttle through vacuum mechanism. A blown fuse and broken wires can be the bane of a CCM mechanism, leading to functional failure and consequently complete speed control failure. In such a case, repairing or replacing the CCM is the only way to restore back functionality.
Actuator Vacuum Diaphragm Leak
The actuator is the device that actually controls throttle through a vacuum mechanism. If the vacuum diaphragm inside the actuator, develops a leak, the cruise control mechanism will fail. This is also one of the most common cruise control problems. The only way out is fixing the leak and restoring vacuum inside the actuator.
Throttle Linkage Breakdown
Throttle linkage is the connector between the actuator and the throttle. These linkages are usually metal chains. If they fail or break down, cruise control will stop working. Replacing the linkage will solve the problem.
Hope this overview of cruise control problems and troubleshooting was useful. Using this 'Auto Pilot' mechanism for speed control comes with its share of risks. These intelligent transport systems need to be used carefully and are most useful in long drives. Troubleshooting cruise control problems is not a simple job, as you might have realized by now. Diagnosing and repairing cruise control problems requires a lot of specialized equipment, to which, you may not have any access. Unless you possess the requisite expertise and tools, it is a job, best left to car repair professionals