The cruise control vacuum reservoir is an air bladder that stores a supply of spare air that is vacuum pressured for when the primary vacuum runs low. This part is located directly behind the front bumper of your car. To understand how this part works, you should understand a little bit about how the engine and cruise control works. The engine in your vehicle creates a vacuum pressure when the pistons are in the down stroke. The air is then drawn into the cylinders and then saved to operate features such as the cruise control.

The servo needs a constant supply of vacuum to maintain its position. If there is more demand for vacuum than the engine can provide, the operations that are run by the vacuum will not work like they should. For example, the cruise control speed will go to excessive speeds or the servo will not stay in the correct position.

The cruise control vacuum reservoir has negative pressure inside of it. Once the RPMs increase on the engine, and the engine vacuum lowers, the reservoir has a good amount of vacuum to ensure the engine has a steady amount to keep the various functions operating as they should.

Over time, the cruise control vacuum reservoir can become broken or fail. If the reservoir leaks or fails, the vacuum pressure will not be able to remain as it should and the other operations will not function properly. The reservoir does not normally get inspected during maintenance, so if you suspect the cruise control vacuum reservoir is going bad, it is important to have a professional mechanic diagnose the problem so they can replace the part.

Since the cruise control vacuum reservoir can fail over time, you should be aware of the symptoms that indicate the part needs to be replaced.

Signs that show your cruise control vacuum reservoir needs to be replaced include:

  • Cruise light on your dashboard
  • Cruise control will not set at all
  • The cruise control surges on its own to mph above where you set it
  • Other features in your vehicle do not work such as the air conditioning, power brakes, or heater

If you are experiencing any of the above symptoms, book a service with a mechanic to replace your cruise control vacuum reservoir.

This article originally appeared on YourMechanic.com as How Long Does a Cruise Control Vacuum Reservoir Last? and was authored by Valerie Johnston.


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