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2009 Mexican Sienna with transponder keys has bad battery

I am in one of those unfortunate moments where I worry that a mistake will turn my 2009 Sienna into a 4000 pound brick if I mess up.

This car has transponder keys, with chips that must be within a few inches of the ignition switch or the car will not start.

The car battery has nearly failed. My question is, does the stored transponder code evaporate when you disconnect the car battery?

I read the owner’s manual, and it only says to make sure you have a radio code if your car has anti-theft radio. So, one would assume that means there is not a problem with changing the battery by traditional brute force means.

However, I have not always found Toyota manuals to be bullet-proof.

Any thoughts or knowledge or experience?

If I cannot be 100% sure, I may try to kludge up wires to the battery cables from my 12 volt charger when I find a 24F battery to buy. The Toyota dealer is several tow hours away.

There is a man a half hour away who has a device which lets him add new keys. I do not know if that will let him save a car that is turned into a brick (a term among electronic technicians.)

I will be Googling a lot before I do anything, but today is also irrigation water day, so time is limited, and thought I’d put the question in the place which will most probably produce answers, or resources. Thanks for any help.

There are times when doing nothing but thinking is the best idea and this seems to be one of them. :smiley:

Rest assured, losing battery power will not affect the key system.

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Maybe your car battery is the problem because its 9 year old

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There is little doubt the battery is bad. When I get it started, the battery voltage read by the scanner runs around 14.0, a little low. And, when I turn the car off, it is in the low 13’s, and continues to sag, all consistent with the bad battery. The question was, will I mess up my car by disconnecting the battery.

Asemaster says it will not, and I have no capacity to doubt him. So, that is the answer I was looking for.

I have read there are cars which can really be messed up by disconnecting the battery, though I don’t know which ones. And, I don’t mean making non-ready the OBD-II monitors, in a place where the complete drive cycle is not possible, nor turning the radio into a brick. But, I know nothing more about this issue, which is why I was concerned. I have figured out I can do the drive cycle, perhaps, on jack stands, if the tires are balanced. I will probably find out soon enough.

One reason I like this forum is because I can keep on learning stuff. I like to learn.

By the way, I have no idea how old the battery is, since the car was purchased used. I will look it over when it is out and see if there is any age data on it. My last battery, purchased for the 2002 Sienna in Texas, lasted less than 3 years.

Some cars do not take kindly to having the battery disconnected. Auto parts store now uses a memory saver when changing a battery after having to pay $1300 for new brains of some sort for a honda. In my case trailblazer actuators fail often after a battery disconnect, my thought the car thinks in relearning the blend doors are in default position, but actually are not.

For short term there is a 9 volt memory saver that plugs into powerpoint to save memory as long as powerpoint is active when keys are off. Another variety plugs into the odb, and has the cig type adapter on the other end, I took an old ac to 12 volt transformer, hooked power to the socket and plug in the memory saver for long term outages. (make sure center is the hot, +12 volts) I have not heard of cars loosing key memory, but that does not mean it can’t happen.

I like the idea of a memory saver, although I have doubts about how long a 9v battery would last. And if 9 volts is high enough. I’d feel better with two 6v lantern batteries in series.

And all the powerpoints in my car turn off when the car is off. So I’d have to use a different connection.

OBD port connectors too that @Barkydog described above. I actually had one for my old T&C van because the one always active powerport stopped working…

Maybe I could plug that memory saver into my … ear? As the years go by some things seem more slippery.

Anyway, as to your car question. I have routinely attached a battery charger to the clamps on my battery cables before I start to remove them from the battery itself. It’s a bit clumsy to work with, and you can certainly attach the ground cable to any solid ground on the frame instead of putting it on the cable end itself. I just leave them clamped while I change batteries, then after everything is snugged up, I remove them. In addition to your concerns, it also saves your clock and stereo settings and keeps the computers from resetting. All in all, it’s been a convenient way to get the job done with a minimum of fiddling around later.

Apparently some chargers won’t put out a current if there’s no battery attached. I don’t understand enough electronics to understand why that’s so. So, no guarantees, but, in the words of Ronald Reagan, “Trust, but verify”. Kind of like raising kids.

My battery charger saw Neandertales, hee, hee. Not really, but it is very old, maybe more than 40 years. Strictly a switch for 6 volts or 12 volts, and a current meter. Works good and I don’t have to wonder what it is doing.

The trust but verify sounds right to me. I marked this solved, but since someone else said something different, I may ask on the Sienna Chat board, just in case. I think asemaster was correct, but just in case!

Battery chargers last a long time. Not much to them. You need to use a fresh 9v battery with the memory saver anyway. Doesn’t last long. The other thing is you have to use a power port that is not key activated, not like what I did on the Acura. Still didn’t do anything except lose the radio. The other thing you can of course do is just hook the charger up to the cables when you pull the battery. It won’t know there isn’t a battery there.

So easy a cave man can do it? Quit picking on neanderthals, can’t spell orangitangs either.

Immobilizer key data is stored in non-volatile memory, if it wasn’t, imagine the number of vehicles towed in each day for key registration because of a discharged or failed battery.

When someone speaks of damaging the “brains” during battery replacement I suspect that they connected the new battery backwards.

I never use a memory saver, I remove and install a few instrument panels each week for airbag replacement and I just write down the radio stations so I can set them again for the customer.

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Yes be nice. DNA testing might reveal a little neanderthal in our/my history. Hey someone has to do the heavy lifting. Lots of weird mixing and matching back thousands of years ago.

I find that practice excellent service but if I had work done correctly resetting my radio selects is not going to upset me.

Having the radio presets doesn’t help if you can’t turn the radio on after disconnecting the battery. That’s why we use memory savers.

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Half of our repairs involve removing the engine or instrument panel so we are not in practice of using a memory saver.

The problems with corrupt radios after battery disconnect that I have experienced were with vehicles from the late '80s and early '90s. Toyota hasn’t used anti-theft codes in the audio receivers since the early 90’s so we don’t have problems with that.

Honda/Acura, Volvo, GM, a simple battery replacement cab turn into an hour long ordeal because the customer never knows what the unlock code is and we have to chase it down by vin, serial number, etc.

I leave it to my guys to use their discretion when to disconnect a battery but it’s not unusual for me to replace an alternator, starter, instrument cluster, or pull an engine without disconnecting the battery.

Happy New Year!

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When I worked at the Chrysler dealer the Mercedes vehicles had security codes for the radios, those codes were available on the computer. I suppose the need for these codes are more time consuming for those outside the dealer network.

Some are more time consuming than others. But even if it only takes 10 minutes that’s 10 minutes we’re not getting paid for to correct a problem that never should have happened and is easily avoided.


I happen to find those memory savers very useful as well, and not just for the radio security codes and/or settings

There have been a few times where a vehicle needed to be jump started, due to a weak battery, and it also needed a smog

Often times, despite the bad battery, the readiness monitors were still complete. So I hooked up the memory saver, replaced the battery, disconnected the memory saver, and proceeded to perform my smog inspection

Sure saved a lot of time

If I had to disconnect the battery on an unfamiliar . . . to me . . . vehicle, I’d consider using the memory saver. At work, we don’t have access to any factory website(s) which will retrieve the radio security codes.