Antifreeze leaks under the passenger side dash?

The problem is heater core.
The heater core needs to be replaced. The heater core is like a mini radiator, providing heat for the interior by coolant circulating from the engine, into the heater core, and back to the engine again. Like a radiator, a heater core can spring a leak, especially with age as a factor. This results in the leak inside the car, which also causes the 'smoke' in many cases, which is actually vapor form of coolant.

For heater core replacing procedure. I suggest you to go through this related help links.Its all complete step by step procedure: ----

How to replace heater core for All car models?

Click the link below: ---

http://technoanswers.blogspot.com/2011/11/how-to-replace-heater-core-for-all-car.html

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How to Flush Heater Core?

http://schematicsdiagram.blogspot.com/2011/12/how-to-flush-heater-core.html

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How to Remove Heater Core ?

http://howtobyme.blogspot.com/2011/12/how-to-remove-heater-core-on-2008-honda.html

Heater Core Replacement?

http://howtobyme.blogspot.com/2011/12/honda-heater-core-replacement.html

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To replace heater core?

http://technoanswers.blogspot.in/2012/02/how-to-replace-heater-core-on.html

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How to replace heater core?

http://technoanswers.blogspot.in/2012/02/how-to-replace-heater-core-on_10.html

How to replace heater core on Buick Regal?

http://howtobyme.blogspot.in/2012/02/how-to-replace-heater-core-on-buick.html

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This will help.Thanks.