Cruise Control Not Working: More Than Just an Inconvenience

Mia Bevacqua
February 21, 2018

cruise control

Cruise control is a major convenience. It lets you travel at a constant speed without working the gas pedal, making it great for long road trips. This handy feature was first installed on Chrysler models in 1958, and now it’s something many drivers can’t live without. 

It might not seem like a big deal if your cruise control stops working, especially if you don’t have to drive long distances very often. But some of the system’s parts can affect acceleration in general — that’s a problem. You’ll want to get it diagnosed by a professional mechanic

Here’s what you need to know in case your cruise control goes out.

How cruise control works

You know the basics — once you’re traveling at the speed you want, you can press the Set button on your steering wheel. There are also buttons to adjust your speed while cruise control is on. And you can cancel it by pressing the brakes (or hitting the Cancel button). But how does it all work?

Older cruise control systems have a cable or linkage that can move the throttle valve, which determines how much air enters your engine — and thus how fast you go. Once you set the cruise control, early versions of the cable or linkage style used an electro-mechanical servo to track the desired speed vs. how fast your car is actually going; more modern systems use a computer. In basic terms, if you climb a hill, the cruise control will open the throttle so your car accelerates. If you go downhill, the computer will close the throttle, slowing the car until it hits that target speed.

Although advanced “adaptive cruise control” is being phased in — allowing cars to respond to changes in traffic speed automatically — most vehicles still use one of two established designs. The first is electro-mechanical and the other is electronic.

Electro-mechanical systems typically include the following components:

  • Control module: Cruise control operation is determined by either the cruise control module (CCM) or the engine control module (ECM) — a computer, in other words.
  • Sensors and switches: The computer makes decisions based on input from, typically, the vehicle speed sensor, brake switch and clutch switch (if equipped). There’s also the control switch, which relays driver input to the computer.
  • Servo: The servo unit operates the cable or linkage attached to the throttle in response to signals from the computer. The servo is attached to the engine vacuum. As the computer adjusts vacuum levels, the servo moves.

Electronic systems also use the same types of computers, sensors and switches. The main difference here is the use of a throttle actuator control (TAC) motor instead of a servo. The TAC is integrated into the throttle body. The computer uses the TAC to open and close the throttle to regulate vehicle speed.

Get it diagnosed by a professional

Reasons your cruise control doesn’t work

Inoperative cruise control is typically caused by one or more of the following problems:
  • Control module problems
  • Sensor and switch issues  
  • Servo problems
  • TAC problems

Control module problems

Problems with the computer: The computer, or control module, is the brains of the cruise control system. A problem with the computer or its circuit can affect cruise control operation. In many electronic systems, this not only includes ECM or CCM, but also the body control module (BCM).

Solution: You’ll want a technician to examine the computer and check for any technical service bulletins. If there aren’t any, the control module may need to be replaced. In some cases, the new module will need to be programmed after installation.

Sensor and switch problems

Vehicle speed sensor problems: The vehicle speed sensor is one of the primary inputs to the computer for cruise control. A problem with this sensor or its circuit can keep your cruise control from working.

Solution: While performing diagnosis, a technician will check to see if the vehicle speed sensor circuit is working properly and repair it, if needed. If the circuit is good, the sensor may need to be replaced.

Brake switch and clutch sensors: The computer cancels cruise control when you press the brake pedal, thanks to the brake switch. In cars with manual transmissions, the clutch switch works the same way. If either of them fail, it can prevent cruise control operation.

Solution: The technician should check that the brake switch and clutch switch circuits are intact, and repair as needed. In some cases the switch may only need to be adjusted. If the circuit is good but the part is problematic, the switch will need to be replaced.

Control switch: If the control switch is faulty, the control module won’t know when the driver is trying to activate the cruise control.

Solution: Again, the circuit should be checked and repaired if necessary. If the switch is still faulty, it will need to be replaced.

» MORE: Get an accurate estimate for your car repair

Servo problems

Servo failure: In an electro-mechanical system, the servo has direct control over the throttle to determine the car’s speed. An internal servo failure will prevent cruise control operation. Usually, the servo also has an integrated position sensor that can cause problems.

Solution: Have a technician check that all connections and circuits are intact. If so, the servo may need to be replaced.

Faulty vacuum and vent solenoids: The vacuum and vent solenoids control servo operation. A problem with the solenoids or their circuit can affect your cruise control.

Solution: The technician should check that the solenoid circuits are intact and working. If the circuits are good but the issue persists, any faulty solenoids will need to be replaced.

Failed vacuum release valve: A failed vacuum release valve will rob the servo of engine vacuum. Cruise control will stop working, as a result.

Solution: Have the vacuum release valve replaced.

Other vacuum-related problems: A working servo is dependent on engine vacuum. A vacuum leak can prevent the servo from getting what it needs. Other vacuum-related problems include a failed accumulator or a bad check valve. Also, an unhealthy engine that’s not creating enough vacuum can affect servo operation.

Solution: Have a mechanic locate and repair the source of low vacuum.

Throttle actuator problems

Problems with the TAC: In an electronic-only system, a problem with the TAC or its circuit can affect cruise control operation.

Solution: Have a technician check that the TAC circuits are all working correctly. If the circuits and sensors are good, the TAC will need to be replaced. In most cases, the computer will need to be recalibrated after TAC replacement.

Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.