When setting your cruise control speed, you don’t consider the behind-the-scenes actions which take place. The engine creates vacuum pressure when the sucking action of pistons in the down stroke draw air into the cylinders. The vacuum pressure is harnessed to operate other features such as cruise control. A servo acts as a vacuum operated switch to hold the vehicle speed steady when cruise control is set. A constant supply of vacuum ensures the servo maintains its position. When there is more demand for vacuum than the engine can supply immediately, operations cease to function as they should. The servo will not stay in the set position, and the cruise control speed will drop or surge to excessive speeds.
To moderate vacuum and to store a cache of vacuum when supply runs low, an air bladder known as the cruise control vacuum reservoir is installed in the system. When your engine is started, there is no initial vacuum and it needs to ‘charge’ the lines and vacuum reservoir. As it builds vacuum, the air bladder has negative pressure inside, or vacuum, that is stored up. When the engine RPMs increase and the engine vacuum drops, the cruise control vacuum reservoir has a storage of vacuum to maintain steady operation of the functions that need it. If the vacuum reservoir has a leak or is cracked, the vacuum pressure will not remain constant and the cruise control will possibly surge to excessive speeds or steadily lose speed.
Your cruise control vacuum reservoir is typically hidden behind the front bumper where it is inaccessible for inspection. It does not require maintenance. If you suspect the vacuum reservoir is cracked or leaking, have it checked by one of our expert technicians and repaired if necessary.
Cruise control is a convenience feature, so its operation is not crucial. If the cruise control vacuum reservoir needs to be replaced, you can do so at your leisure.
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