* Exhaust Leak: This is the most probable cause. A leak in the exhaust system, anywhere from the manifold to the tailpipe, can allow exhaust gases to enter the passenger compartment. The smoke you see is likely unburned fuel or oil burning in the leak. The location of the leak will influence *where* you smell the exhaust most strongly (near the engine, under the car, etc.).
* Catalytic Converter Issues: A failing or clogged catalytic converter can overheat and cause smoke. This is usually accompanied by a rattling sound and reduced engine performance. The smell might be more sulfurous than a simple exhaust leak.
* Head Gasket Blowout: A blown head gasket allows coolant to mix with combustion gases. This can create a white or milky smoke and a sweet smell (from the coolant). This is a very serious issue requiring immediate repair.
* Cracked Engine Block or Cylinder Head: Similar to a blown head gasket, cracks allow coolant or oil to enter the combustion chamber, leading to smoke. This is a major engine problem.
* Valve Cover Gasket Leak: While less likely to cause *exhaust* fumes inside the cabin, a leaking valve cover gasket can allow oil to leak onto hot engine parts, causing burning oil smoke. This is usually accompanied by a strong oil smell rather than exhaust.
It's extremely dangerous to drive a car with exhaust fumes entering the cabin. Carbon monoxide poisoning is odorless, colorless, and deadly. Do not drive the car until the problem is diagnosed and repaired by a qualified mechanic.
The best course of action is to have a mechanic inspect your Grand Am immediately. They can pinpoint the source of the leak and smoke and provide the necessary repairs. Ignoring this problem could lead to significant engine damage or even injury.
