When To Use the “Power” Button (Automatic Transmissions)

Since about 1980 all—well, almost all—automatic transmission cars have had a button or switch somewhere marked “Power”. Sometimes it is on the transmission selector shaft, sometimes on the steering column, sometimes on the dash, or it maybe located behind or in front of the transmission selector on the centre tunnel somewhere.

In some cars Power mode might have another name such as Sports mode.

The thing with“Power” mode is that it does not make your engine more powerful.

What is does is change the decisions your automatic transmission makes about when it will change gears—which has nothing to do with the amount of power your engine is putting out. Hence the reason manual transmission cars don’t have a “Power” mode button anywhere; because manual transmission drivers are supposed to work it all out by themselves and know exactly when to change to the required gear ratios.

When the “Power” button is not engaged the automatic transmission changes gears according to its normal programming. The normal gear changing program is generally set to provide you with a comfortable driving experience while delivering the best possible fuel usage. Some automatic transmissions do this well and others no so well.

With the “Power” button engaged the programming for the automatic transmission is changed to a program where optimal fuel usage is no longer an overriding consideration. In power mode the automatic transmission will hold gears longer as it changes up during take-off and acceleration. It will correspondingly change down to a lower gear sooner, at a lower torque sensitivity, than it would normally in those cases where it detects the need to change down—for such things as overtaking, going up hills, or travelling slowly, etc.

Basically, with the transmission in power or sports mode the transmission becomes more ‘edgy’.

So when should you engage power mode on the transmission?

Most motor vehicle owner’s manuals recommend you engage power mode:

1. when towing a medium to heavy load,
2. when driving through hilly terrain,
3. when about to overtake on the open road,
4. when driving in stop-start city traffic, or
5. when driving in conditions where your speed is frequently under 30 mph/50 kph.

Other manuals may include other times to use power mode such as when there are three or more people in the car (because of the increased weight; usually only applies to smaller cars with smaller engines), travelling on sandy roads (because of the increased rolling resistance caused by the sand), or driving along a beach (which is the same reason as travelling on sandy roads).

Why?

Well, in the case of point 1, it should be pretty obvious why a gearbox re-tuned for power would be needed when towing medium to heavy loads.

For point 2, engaging power mode in hilly terrain will stop the transmission from gear hunting as much going up inclines. In power or sport mode the transmission will generally just stay in the final drive gear and will not shift into over-drive. Going into over-drive going up a hill is folly (i.e., stupid) but many transmissions will do this in normal mode because they don’t know any better. But then they no sooner get into over-drive and they find they need to drop back to final drive (i.e., top gear), and then they think they can go back to over-drive again. And so on. And this is what is known as ‘hunting’.

So using power mode going up an incline will cause the transmission to hold top gear and not slide up into over-drive; thereby providing a smoother even ascent of the incline. And should the incline be challenging enough to require more power than top gear provides then the transmission will change down to the next lowest gear sooner rather then later—thereby avoiding the car losing too much power going up the hill.

With overtaking on the open road, point 3, it should be pretty clear why putting the transmission into power mode is a good idea. The general idea with overtaking is to get past the vehicle in front as quickly and as safely as possible.

With power mode engaged, when you decide to make your move the transmission is going to drop the over-drive ratio and fall back to top gear much sooner and cleaner. Ditto if a gear lower than top-gear is called for. In fact on a four shift automatic transmission—with three drive gears and one over-drive ratio (e.g., 1, 2, 3, D)—a well programmed transmission in power mode will most likely instantly shift down two gears on the first shift as you start to overtake—but this will depend on how sharply you apply the accelerator, whether you are overtaking up an incline, and what speed you are doing when you start to overtake.

The reason for engaging power mode in stop-start city traffic, point 4 above, is not quite as obvious as points 1, 2, and 3.

There are two reasons for doing this. The first is that, by and large, you have more control of a car in lower gears. So, by engaging power mode you will likely be causing your transmission to favour staying in a lower gear, rather than always trying to hitch itself up to a higher gear—which is what it does in normal mode (because it is trying to save petrol).

Secondly, as the transmission set in power mode is going to be relatively content staying in a lower gear, you will stop the transmission from gear hunting—going from over-drive to third to over-drive back to third to second to third, etc.— so much in the crawling stop-start traffic.

The reasoning behind the final point, point 5, is much the same as for point 4. In relatively slow moving traffic engaging power mode will generally stop the transmission from hunting between gears (over-drive and top gear), and because it will stay in top gear you will have more driving control. Due to over-drive not being engaged you can stop more quickly should you need to stop, and if you need to speed up marginally quickly then the transmission is already out of over-drive (most likely) so the engine, and thereby the car, will be more responsive more quickly.

Okay … I really didn’t mean that post to be quite that long. I probably should not have put in all that explanation about the five points. Oh well. It’s there now.