If you disconnect your battery will your settings for things like radios, clocks, etc. be lost?

Dear Car Talk

Dear Car Talk | May 01, 2000

Dear Tom and Ray:

There's a guy named Bob Sikorsky who has an automotive column that I've seen in some other papers. This past week, he was asked the following question: "I've heard that, when a battery is disconnected in a newer car, all memory functions, such as clock and radio settings, engine codes, and the like, are lost. Is this true?" Sikorsky's answer was: "If a battery is disconnected for any length of time, all computer storage functions ... are lost and must be reset after the battery is reinstalled. There are portable, battery-fed devices that plug into the cigarette lighter housing and provide trickle current to these units while the main battery is disconnected, keeping those settings from being lost."

You covered a similar topic in your column regarding lost settings after a battery replacement. You mentioned that the computer is supposed to "automatically relearn" the correct settings from the engine sensors once the car has been taken for a sustained, moderate-speed drive. So, which is true? Are the settings lost forever, or are they automatically relearned? I'm planning to change the battery soon on my '97 Camry and want to know what to do. Thanks. -- Larry

RAY: We're both correct, Larry. We were talking about two different kinds of settings.

TOM: Bob Sikorsky was talking about the clock and the radio presets. Those aren't really "computer" settings. Those are memory settings in specific "stand-alone"
devices. And those WILL be permanently lost if the battery is disconnected. To prevent the loss, you can use a little 9-volt device like Bob describes.

RAY: We use one in our garage, mostly because it would take us a year and a half to reprogram most modern radios, and probably another three months to figure out
how to reset the clock.

TOM: What WE were talking about in our column were the ENGINE settings that the engine-management computer stores. These have to do with things like engine
timing and automatic transmission shift points.

RAY: And if you disconnect the battery, those settings will be lost. But if you just drive for five minutes or so at about 35 mph, they will all be completely relearned.
Then you can pull over for a couple of hours and work on the radio.

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