What to know about the Cruise Control Vacuum Reservoir:
When setting your cruise control speed, you don’t consider the behind-the-scenes actions which take place. The engine makes vacuum pressure when the sucking action of pistons in the down stroke draws air into the cylinders. The vacuum pressure is harnessed to run 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 continuous 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 fitted 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 storage of vacuum to maintain steady operation of the purposes that need it. If the vacuum reservoir has a leak or is fractured, the vacuum pressure will not remain constant and the cruise control will possibly surge to excessive speeds or steadily lose speed.
Facts to Note:
Cruise control is not the only system that uses the engine’s vacuum. Power brakes also use the engine vacuum and heater controls at times.
How to Fix:
The cruise control vacuum reservoir is confirmed that it needs to be changed. The vacuum line is then disconnected from the reservoir.
The faulty Cruise Control Vacuum Reservoir is detached.
The new Cruise Control Vacuum Reservoir is fixed.
The vacuum line is linked to the reservoir. The Cruise Control Vacuum Reservoir is tested for operation by starting and checking for leaks.
The vehicle is road tested for proper operation of the Cruise Control.
Your cruise control vacuum reservoir is typically hidden behind the front bumper where it is unreachable for inspection. It does not need upkeep. If you suspect the vacuum reservoir is cracked or leaking, have it checked by one of your expert technicians and repaired if necessary.
Common symptoms indicating you may need to change the Cruise Control Vacuum Reservoir:
Cruise control surges to speeds well above the set cruising speed
Cruise control will not sustain speed and drops well below the set speed
Nausea-inducing surge can be felt when the cruise is set
Other vacuum-operated features such as power brakes, air conditioning, and heater control are functioning improperly
Importance of this service:
Cruise control is a convenience feature, so its operation is not crucial. If the cruise control vacuum reservoir needs to be changed, you can do so at your leisure.