This is a 2003 Honda Odyssey in the process of having the heater core replaced. The whole dashboard must be removed to access the heater core. A heater core typically ends up needing replacement due to poor cooling system maintenance. It either gets clogged with sediment and you have no heat or it leaks antifreeze into the cabin due to corrosion. Symptoms of a leaking heater core are a bad smell in the car and or fogging of the windows. We recommend having your cooling system (antifreeze) replaced or flushed every 30,000 to 60,000 miles depending on the circumstances.