Some problems are under your nose. You can detect them by their odor:

• The smell of burned toast — a light, sharp odor — often signals an electrical short and burning insulation. To be safe, try not to drive the vehicle until the problem is diagnosed.
• The smell of rotten eggs — a continuous burning-sulphur smell — usually indicates a problem in the catalytic converter or other emission control devices. Don’t delay diagnosis and repair.
• A thick acrid odor usually means burning oil. Look for sign of a leak.
• The smell of gasoline vapors after a failed start may mean you have flooded the engine. Wait a few minutes before trying again. If the odor persists, chances are there’s a leak in the fuel system — a potentially dangerous problem that needs immediate attention.
• Burning resin or an acrid chemical odor may signal overheated brakes or clutch. Check the parking brake. Stop. Allow the brakes to cool after repeated hard braking on mountain roads. Light smoke coming from a wheel indicates a stuck brake. The vehicle should be towed for repair.
• A sweet, steamy odor indicates a coolant leak. If the temperature gauge or warning light does not indicate overheating, drive carefully to the nearest service station, keeping an eye on your gauges. If the odor is accompanied by a hot, metallic scent and steam from under the hood, your engine has overheated. Pull over immediately. Continued driving could cause severe engine damage. The vehicle should be towed for repair.