• The most common reasons for emission test failures include: a malfunction in the components of the vehicle that regulate the fuel/air ratio such as the oxygen sensor and the EGR valve; a dirty air filter; misfiring spark plugs; leaks in the vacuum system; or a poor-fitting fuel cap. Many of these components can be checked and repaired during routine tune-ups. Follow the manufacturer’s recommended maintenance schedule.
• Have your oil changed regularly.
• Replace your fuel cap securely after filling up. On 1996 and newer model year vehicles, the “Check Engine” light may illuminate as a result of a loose fuel cap. If the “Check Engine” light is illuminated, try tightening the fuel cap until it clicks, then drive the vehicle until the light turns itself off. If it does not turn off, take your vehicle to a qualified repair technician.
• Keep the sealing surfaces of your fuel cap clean and in good condition.
• Keep your tires properly inflated.
• Check belts and hoses for wear.
• A transmission problem is directly related to the emission control system and can trigger the “Check Engine” light. A diagnostic analysis will yield a transmission code that will help identify the transmission component(s) needing repair. Transmission malfunctions can prevent a vehicle from running efficiently, increasing emissions above federal certification limits.
• Before seeking repairs, research any recalls, technical service bulletins (TSBs), and manufacturer warranties regarding your emission control system.



• Avoid high traffic times such as before work, after work, or during your lunch hour, if possible.
• Avoid the first few days and last few days of the month, Mondays, and the day before or after any holiday.
• Stick to the middle - the middle of the month, middle of the week, mid-morning or mid-afternoon.