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new battery / smart keys NOT working

Discussion in 'Gen II Prius Care, Maintenance and Troubleshooting' started by monolisp, Jul 27, 2009.

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  1. monolisp

    monolisp New Member

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    Your Vehicle Year:
    2005 Prius
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    Hi there,

    I am hoping someone can help me with my 2005 prius with smart keys. I started having trouble with the electronics (slowly the smart keys stopped working) along with some other strange phenomenon. I took the car to the dealership and they told me I needed to replace the aux battery in the rear. I did so, replacing with an OEM from Toyota dealership. The trouble is the smart keys still do not work with the car and I am wondering if there is anything I am missing? Do they need to be reprogrammed after the installation of a brand new battery? Has anyone had any similar problems? I had the bettery tested by another shop and they confirmed that it was indeed bad. Any help would be greatly appreciated!
    :confused:
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I suggest that you replace the fob battery to make sure that a worn battery is not an issue.

    If the system still doesn't work, then find the SMART button located near the steering column, and press it to see if that helps to activate the system again.


    If the SMART system still doesn't work, then you'll have to seek dealer assistance. Note that the SMART and immobilizer ECUs are programmed to recognize the fob, not the reverse.
    1 person likes this.
  3. HelpSaveMotherEarth

    HelpSaveMotherEarth New Member

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    someting that i just found out im ordering the 2010 iv with solar roof...but if the key dies then its got a key that slide outs to OPEN the doors but WILL NOT start the car...so if the key is dead you can get in the car but it will not start...
  4. JasonPro

    JasonPro Junior Member

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    Actually, the smart key is a very short range passive transmitter. If you hold the powerless smartkey up to the power button it will be powered by the car in order to transmit it's authentication. It reminds me of the contact-less badge that my company and many others have to use at work to open doors. So, you just hold your key up to the power button very close and then press power. It should work without a battery. That is my understanding at least.
  5. Joannerice

    Joannerice Junior Member

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    Your Vehicle Year:
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    Model:
    Three


    I just started having this problem today. Smartkey will not lock or unlock the car. Tried two batteries and nada. Made sure button under the steering wheel was in proper position. NADA. I can the start the car okay with putting the fob into the key slot so no problem driving the car, but it is PITA to get the little key out to open the door.

    Just out of curiosity, I tried what the above poster said and it did not work for me. The only way the car will start is with the fob in the key slot.

    1) Have the prices on new smart keys come down at all? Am I looking at $300 to $500 for a new one?

    2) Also, in researching the problem here, someone mentioned a red light on the fob. Where would that red light be?

    Thanks.
  6. 2009Prius

    2009Prius A Wimpy DIYer

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    To the right of the "lock" button. When you push either the "lock" or the "unlock" button the red light flashes.
  7. Joannerice

    Joannerice Junior Member

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    Thanks. I just tried it and no red light.
  8. RobH

    RobH Senior Member

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    It's getting complicated around here...

    The Gen2 (2004-2009) has a switch on the lower dash that can disable the proximity function of the smart key. The Gen3 (2010+) doesn't have the switch, although it will turn the proximity function off if the car is left unused for several days.

    The Gen2 has a slot in the dash. The Gen3 doesn't have the slot, but it has a similar function when the key is held near the Power button. The reason both Gen2 and Gen3 have these functions is to handle the situation when the battery in the key loses power. When the key battery isn't working, the keyslot/Power button transmits enough power to the key for it to send its identification. The range is only a few inches.

    Both Gen2 and Gen3 keys have a red LED that lights up when a button is pressed on the key. The LED also lights up when the key is recognized near the outside of the car when the car is turned OFF and locked.

    There are two different Gen2 systems. The basic one has a black logo on the back of the remote. It does not have the proximity functions. The smart remote (SKS) has a silver logo on it, which indicates that it has the proximity functions. All of the Gen3 systems sold to date have the SKS system.

    If the red LED doesn't flash when a button on the remote is pressed, then the battery isn't providing enough power. It could be dead, inserted backwards, or corrosion could be interfering. The remote is quite durable, so it's very unlikely that it would be damaged by dropping. If it gets wet, that could could be a problem. If it was just clean water, waiting for it to dry should be enough. Salt water is damaging, and will have to be rinsed out with clean water at the minimum.

    The car warns of a weak remote battery by sounding a single beep when the car is powered down.

    When the 12 volt battery in the car gets weak, all sorts of strange things can happen, including problems with the smart key system. The 12 volt battery typically lasts about five years. If you have to replace the 12 volt battery in the car, it would be a good idea to also replace the batteries in the remotes.

    All Gen2 and Gen3 remotes have a small physical key. It can be used to lock/unlock the driver's door. It cannot be used to start the car.
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  9. Joannerice

    Joannerice Junior Member

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    I had a new 12 volt put in 2 years ago (3 1/2 years after purchase). I, or someone, left the interior lights on and started draining the battery. Then all kinds of funny things happened and people here and the dealership said to replace it, which was done.

    I'll try getting another battery for the FOB. The two I tried were from the same packet and have been in the glove compartment for a while. I know it is inserted correctly. There is an excellent video on how to do it on Youtube. Guy at the Toyota replaced one battery in the FOB and then I replaced that battery with the second one.
  10. Hans18

    Hans18 New Member

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    ----USA ONLY----
    I had one smart key not working and replaced the battery, but still it was not working, then I noticed that the red led was not responding when I pushed the button, so I went through a stack of batteries and found out that the new ones do not work 3.28V, but the ones that had 3.1V worked, so it looks the electronics works not if the battery voltage is above 3.1V. So the solution was to discharge the battery to 3.1V and now the Smart key works. (Operating range is 3.1V-2.9V for the Smart Key 2004 model)
  11. grifter07

    grifter07 New Member

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    i replaced the smart key battery and it didnt work after i changed it out. red light on key was blinking and everything. apparently the key is connected to the 12v battery. If you go to your trunk where your 12v battery is and disconnect the black wire for a few moments, after you reconnect the wire, the key may start to respond again to locking and unlocking the car. Thats what i did and it worked for me.
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