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Old 06-13-10, 09:11 AM   #1
e-man
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Default Will car start if key FOB battery dies?

Hey guys. Strange question. I believe the Lexus key has a security chip in it that needs to be in close proximity to the ignition in order for the car to start (right?). If the battery in the key FOB dies, will the car still start with that key? Or, is the security chip in the key independent of the key FOB battery? Thanks for your help.

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Old 06-13-10, 09:40 AM   #2
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if it's for your 99 all you have to do is manually unlock the doors and it will disarm the alarm and start the car.
I am not sure if you HAVE to do it but in my 99 GS400 this arms the alarm and disarms it manually when the battery went dead once. (battery in the fob, not the car!)
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Old 06-13-10, 09:55 AM   #3
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Originally Posted by ar15guy View Post
if it's for your 99 all you have to do is manually unlock the doors and it will disarm the alarm and start the car.
I am not sure if you HAVE to do it but in my 99 GS400 this arms the alarm and disarms it manually when the battery went dead once. (battery in the fob, not the car!)
Right, but assume the car is unlocked. Does the security chip in the key FOB function properly if the key FOB battery is dead? In other words, if the key FOB battery is dead, and the car is unlocked/disarmed, will the car start?

The reason I ask is because I've been having intermittent trouble starting my car, and I noticed that my trunk doesn't always open on the first try with the key FOB, and I'm wondering whether the two issues are related.

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Old 06-13-10, 10:45 AM   #4
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Yes. Your car will still start even with a dead fob battery. Its no different than using a valet key.
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Old 06-13-10, 10:51 AM   #5
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Yeah what bigL said. However, on my friends 1991 LS400 he has the issue where his battery has never worked since he got it and there have been at least a few times out of the month (every month) where he unlocks the car with the key and tries to start it but no luck.
We figured it's something with the door lock actuator/alarm. The reason being if he gets out unlocks/locks with the key and gets back in it starts right up.
Not sure about your trunk issue that may just be a faulty button.
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Old 06-13-10, 11:05 AM   #6
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Originally Posted by e-man View Post
Right, but assume the car is unlocked. Does the security chip in the key fob function properly if the key fob battery is dead? In other words, if the key fob battery is dead, and the car is unlocked/disarmed, will the car start?

The reason I ask is because I've been having intermittent trouble starting my car, and I noticed that my trunk doesn't always open on the first try with the key fob, and I'm wondering whether the two issues are related.
The chip is a resistor - it does not require power in order to allow the engine to start. The ignition expects a specific resistor to be present in order to start the car, nothing more. The fob battery being dead has nothing to do with it.

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Old 06-13-10, 06:12 PM   #7
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Quote:
Originally Posted by e-man View Post
Right, but assume the car is unlocked. Does the security chip in the key FOB function properly if the key FOB battery is dead? In other words, if the key FOB battery is dead, and the car is unlocked/disarmed, will the car start?

The reason I ask is because I've been having intermittent trouble starting my car, and I noticed that my trunk doesn't always open on the first try with the key FOB, and I'm wondering whether the two issues are related.

e
Replace the battery already - $3.99 and 2 minutes of time.
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Old 06-13-10, 10:34 PM   #8
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The battery in my key died before and my car started up just fine. You can find the batteries in the watch section of Wal-Mart. I bought like 3 extra and stocked up.
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Old 06-14-10, 02:15 AM   #9
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The battery code is CR1616 3V if that helps.
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Old 06-14-10, 08:58 AM   #10
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Quote:
Originally Posted by Big Mack View Post
The chip is a resistor - it does not require power in order to allow the engine to start. The ignition expects a specific resistor to be present in order to start the car, nothing more. The fob battery being dead has nothing to do with it.

Big Mack
Big Mack, I think you are confusing the systems in our Lexuses to that of the GM VATS system that uses RESISTORS on the shaft of the key. Those required actual CONTACT to be made with the resistors when the key was inserted. Ours use a TRANSPONDER chip that doesnt required contact and power. The transponder chip gets energized everytime it gets used so there is no battery required for the chip.

I'm very familar with this sort of stuff because my company has to deal with these systems quite often. We are an authorized Pro-Series Compustar dealer in our area.
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Old 06-18-10, 10:40 PM   #11
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Big Mack, I think you are confusing the systems in our Lexuses to that of the GM VATS system that uses RESISTORS on the shaft of the key. Those required actual CONTACT to be made with the resistors when the key was inserted. Ours use a TRANSPONDER chip that doesnt required contact and power. The transponder chip gets energized everytime it gets used so there is no battery required for the chip.

I'm very familar with this sort of stuff because my company has to deal with these systems quite often. We are an authorized Pro-Series Compustar dealer in our area.
Bad choice of word on my part. The transponder chip is a digital code, not a resistance. Thanks for the clarification, mang!

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