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Why does my clock keep resetting itself?

you came from: Master List > Body Electrical



It's simple: the "Backup" fuse is blown. And the fix is simple too: replace the fuse.

Despite the name, this fuse has nothing to do with those white reversing lamps at the rear of the car; it has to do with providing a "keep-alive" electrical IV-drip to certain devices that require it  in order to be able to remember things.

The clocks on your microwave and stove, or the clock radio in your bedroom, need a steady source of power to remember what time it is.
The house power goes out because of a thunderstorm, and the clocks lose their memory and think it's 12:00 again, requiring you to go around the house resetting them all back to the real time.

Your car's clock is the very same, only it gets its power from the car's main lead-acid battery, not wall current.
Power can be fed from the battery to the clock through the ignition, such as when the engine is running, or from a separate "backup" feed from the battery when the engine is off. Along with the clock, there are a number of other things that need this steady, engine-off electrical current to keep their memories intact, such as the engine and automatic transmission computers (plus the radio, which would otherwise display "CODE" on its readout, meaning you need to enter the security code to get it working again). This engine-off current is called the "backup" current. And this "backup" current passes through the "Backup" fuse, which can fail.

(In Canada, this fuse may be called "Backup/Hazard", and would control the hazard warning flashers as well. So if your Canadian car's hazard lights don't work, now you know why.)

Should the "Backup" fuse blow, not only will the clock reset, but the engine's and transmission's computers will also forget everything they know each time you shut the car off. This you will be unlikely to be aware of, though, since you won't likely see or feel any obvious symptoms. However, if your state/province does its emissions testing by plugging an OBD-II tester into the diagnostics port, you'll discover then that most of the OBD-II "readiness monitors" will report "not ready" and you'll fail the test. So if your clock is losing its setting, that's a sign that lots of other stuff isn't working right either.

So where's the fuse? Its exact location varies, but it's always in the underhood fuse box atop the right-side shock tower, and it's always one of those flat, colored-plastic 7.5amp or 10amp two-legged fuses. I've found it's usually at the extreme rear, outside edge of the fuse box. If the sticker is still on your fuse box, Bob's your uncle. If it's missing (and it often is after many years) all you can do is consult your factory repair manual, or start pulling fuses one by one until you find the blown one.


Rear of clock, showing pinouts
This is the rear of a typical Honda clock which is separate from the radio unit. There are four electrical pins. The pin highlighted in red is the one that provides "backup" power to the clock in the absence of ignition current. This is the one that passes through the "backup" fuse.

The "ignition" feed is what makes the clock display turn on when you start the car.

The "headlight switch" signal is the one that tells the clock to dim its display, so it won't be too bright at night when you have your headlights on.