If your vehicle is showing sweet, maple syrup-like smell coming from the vents, here are the most likely causes and the parts you'll need to fix each one.
The heater core is a small radiator behind your dashboard that provides cabin heat. When it corrodes or cracks, sweet-smelling engine coolant leaks directly into the ventilation system and is blown out of the vents.
The rubber hoses or plastic connectors that carry coolant from the engine to the heater core can degrade and leak near the firewall. The sweet-smelling vapor is then drawn into the cabin's fresh air intake.
If the heater core or hoses were recently replaced, a loose hose clamp or pinched O-ring at the firewall connection will cause coolant to leak into the cabin or cowl area.
Some vehicles use a valve to control the flow of hot coolant into the heater core. If this valve develops a leak near the cowl, the blower motor can pull the evaporating coolant vapor into the cabin.
A failing head gasket can force high-pressure exhaust gases into the cooling system. This extreme pressure can rupture the heater core or force coolant out near the cabin air intake, causing the smell.