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Discussion Starter · #1 ·
Hi, all,

This may be only my second time in 5 years asking for help or opinions here. For the last 2 or 3 days when I try to enter my 2005 Prius with the smart key system, the system won't cooperate & the fob buttons don't open the car either, so I have to resort to getting the metal key out of the fob to enter. Once inside I get the missing key symbol & the car refuses to start unless I slide the fob into the docking station.

The fob battery for the only one I use is the original (I have to find that safe hiding place where I stored fob #2 five years ago) and the 12 volt battery is still the original too. After I have driven the car for about 1/2 to one hour the SKS works fine for entering & starting the car. It only refuses to work for getting in & starting first thing in the morning or after a short 5 mile ride, so I'm thinking that rather than the fob battery being at fault that it's actually the 12 volt battery. It's probably low from sitting overnight & doesn't have enough power to sense the fob presence or to actuate the door locks. Then after driving at least 1/2 hour or more, the 12 volt sufficiently recharges for the SKS to work fine the rest of the day.

Looks like the purchase of a new 12 volt battery might be in my immediate future. I'll have to get the self-test battery strength procedure (that Jeff Denenberg always posts) out & see if it confirms my suspicions about my 12 volt battery. Do any of you guys & gals kind of agree with my diagnosis before I do the actual self-test?
 

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The cheapest approach is to replace the fob battery. If that doesn't correct the problem, then the 12v battery replacement is the next step. Based on the age of the batteries (5 years), both the fob and 12v battery should be replaced. Remember, a dead 12v battery can cause a lot of problems (for you) if it dies at the wrong time or place.
 

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Discussion Starter · #3 ·
Hi, firepa63 & any others who may be looking in,

I did Jeff Denenberg's self-test. The battery voltage flickered between 12.5 & 12.4 volts (no load), but dropped to 12.2 volts upon entering "IGN. on" state (under light load). For ha, ha's I turned on the HID headlights & the reading dropped to 11.8 volts (but that's a lot of juice that the HID's use, isn't it?). When I went to "READY" status the reading went up to 14.4 volts.

Do you still think it's mainly the fob battery rather than the 12 volt battery. I'll definitely try the fob battery 1st because of course that's the cheapest item to start with to see if it turns out to be the cure. 94,000 miles & 5 years is a lot of time for any battery (fob or 12 volt). I'll keep you informed as soon as I learn something.
 

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Discussion Starter · #5 ·
Hi, guys & gals.

Just a quick update. I changed the fob battery yesterday. That's all that was needed to make everything good. In looking at my owner's manual to find the stock # for the battery, I saw a diagram of the remote & noticed that I forgot all about that little indicator light (I never see it because I have my remote inside a leather cover sold by one of the vendors who is a member here). That little light wasn't blinking with any pushes of any of the buttons, so the fob battery was most likely totally dead. Thanks firepa63, for your responses.
 

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Ken, usually when the fob battery is going bad, you will hear 1 long beep when powering down the car. Did you notice that beep before replacing the fob battery?
 

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Discussion Starter · #7 ·
Hi, firepa63,

Yeah, now that you mention it I do think I remember hearing a long beep a couple of times, but I think it was as I was locking the doors & thought it was because I had left a door ajar (but didn't find one ajar any of the times) or left the power on & tried to lock, but then realized that the long beep wasn't preceded by 3 short beeps as I closed my door (so it wasn't a "forgot-to-power-down" situation).

Now that I've gone through the 12 volt battery strength self-test once (with a cheat sheet), I can do it almost blind folded, so that will probably start to be a once per week check to monitor its strength (to proactively judge when to get a new 12 volt) so I don't have a complete failure & get myself stranded somewhere. Blessings to Jeff Denenberg for originally posting that procedure & to Richard Schumacher for clarifying it. Knowing how to do the dance to get into that self-test display has the potential to be a real life saver. That cheat sheet page is going into my manual in case of an emergency. (Power to the people who are informed).
 

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If your 12-volt lead-acid batt is 5 years old or more and you don't want the car to be stranded and require a jump to start it at some random unexpected time and place then you should replace that batt. There is no warning of impending doom. The car may be working normally but then refuse to start at some random time and place which could constitute an imposition or a serious issue depending on where and when the car is stranded.

The 12-volt lead-acid batt powers the dash (all the electronics) so you can't start the car. The "savings" you think you are getting by trying for 6-7 or more years of service from the 12-volt batt will seem insignificant if you are stranded and inconvenienced.

I have a battery load tester and recommend its use to keep track of the 12-volt batt condition. This allows you to be in a position of knowledge regarding batt condition. You can then change the batt when it begins to show signs of weakening and impending failure rather than gambling and getting stranded. My wife was stranded 30 miles from home O N C E but never again.

Patrick
 
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