The idea behind cylinder deactivation theory on modern engines, sometimes referred to as multiple displacement, displacement on demand (DOD), or (VCM) variable cylinder management, is that certain cylinders deactivate during low power situations. Controlled by a primitive computer by today’s standards.

The Cadillac L63 V-8-6-4 engines were the first to try that, if I remember correctly in 1981, and I think Mitsubishi had a system in place by 1982. Although the idea was finally able be to put into production usage in the mid to late ’90s’s with success, engineers still work to improve such systems.

Cylinder Displacement technology deactivates some of the motors cylinders when they are not needed. Through an on-board computer, the engine picks up signals from sensors and switches, which tells the engine when to deactivate cylinders under low load conditions to save fuel. Of course it has to work the other way too, if you need more power to pass a car, the proper amount of cylinders will be commanded.

In retrospect, DOD was not very successful and proved to be more trouble than it was worth in the beginning. But it was one of the first attempts to be creative and use some new technologies to improve fuel mileage and performance. When you consider the ultra complicated computerized systems we use today in modern automobiles to improve mileage and performance, cylinder deactivation technique was a noble first step.

We tend to think these systems are complicated and scary, and they are. That is why the mechanic of today has to be smart, literate and be able to comprehend directions. One of the issues we are staring at is that not much information is available about these systems anymore. When you consider that most of the mechanics that really knew how to fix an older cylinder deactivation system may be retired, it is easy to see why it may be difficult to get effective repairs performed on the old systems. As long as new, young mechanics enter the auto repair field and information is available, the job can be done.

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