8 Important Smog Test Tips
1. Running Right - Do not subject your vehicle to a Smog Inspection if it does not run right. Chances are that it will fail the smog check and you will lose your inspection fee. Seek repair assistance first. This will save you time and money, and ensure your vehicle will pass the smog test.
2. Take a Drive - Drive your vehicle for at least 20 minutes prior to arriving at the smog station. This will ensure your vehicle is properly warmed up and is running at it's optimum level. Remember your engine is a fuel burning machine. To ensure proper combustion it needs to have sufficient time to warm-up and this can be accomplished through driving for at least 10 to 15 miles.
3. Use Additives - The use of fuel additives can be very helpful in lowering emission levels and helping your car, truck, van or SUV pass the emissions inspection. Fuel additives are generally poured into a vehicle's gas tank during fuel refueling. The additive is mixed withyour vehicle's fuel. The purpose is to clean carbon deposits within your engine's intake and exhaust paths, allowing for both fuel and air to flow freely within its passages, thus lowering emission levels, improving combustion, increasing overall engine performance, and helping you pass the emission test. These types of products offer helpful solutions to various vehicle emission and smog test problems.
Note: Read your fuel additive's instructions regarding having your vehicle smog tested while using the additive. Fuel system additives and fuel system treatments require using the complete application and refueling with fresh fuel prior to the smog check.
4. Inflate Tires - If your vehicle is model year 1999 or older it will be driven on a dynomometer while a sample of its exhaust is collected by the smog machine. Making sure your vehicle's tire pressures are even and correct will allow the vehicle to be driven with greater stability and accuracy during the smog exam. This will improve the overall emissions output of your vehicle by allowing the engine to maintain a constant and steady load. Correct and even tire pressure may be the deciding factor between a borderline vehicle failing or passing the smog test. This passing tip, as well as tips number 5 and 7 do not necessarily apply to your vehicle if it's 2000 model year or newer; this is not to say your vehicle's tires shouldn't be properly inflated, of course.
5. Change Oil - If it's close to your next oil change interval, go ahead and do it before the smog check. The PCV (positive crank ventilation) system of your vehicle is designed to allow your engine to breath fumes located in oil compartments (oil pan, ect.). The fumes are then burned through the combustion process. If the oil in your engine is contaminated due to inadequate oil changes it may very well cause your vehicle to fail the inspection.
Contaminated oils are high in Hydrocarbons (HC) and will present a rich mixture to the engine chambers. Avoiding oil changes not only causes pre-mature engine wear but can also cause your vehicle to fail the smog inspection. Change the engine oil.
6. Check Engine Light Off - Make sure your vehicle's Check Engine Light or Malfunction Indicator Lamp is not illuminated. A constantly illuminated Check Engine or MIL light is an automatic smog failure. A certified repair shop can diagnose the check engine light condition and offer you an evaluation and estimate. The home mechanic may also diagnose a Check Engine light malfunction via special Check Engine codes retrieval tools, available at most auto parts stores. Note: A smog technician can not refuse to test your vehicle based on the fact that he or she notices an illuminated light. The smog technician must perform the smog check and fail your vehicle. This is California State law. Be aware. Get a pre-test.
7. Battery Recently Disconnected? - If your vehicle recently needed a jump start or battery replacement we recommend holding off on getting the smog check for at least one week. Whenever a vehicle's computer (engine control unit) losses power, such as when it's battery has been disconnected or charge depleted, its internal self-test monitors are erased. Without these required Emission Monitors your vehicle can not pass the smog test. You will be required to drive between 100-200 miles and over the course of a week, called a Drive Cycle, in order to "complete" the emission monitors and be allowed to pass the smog check.
8. Avoid Rainy Weather - If your vehicle is model year 1999 or older it will be driven on a dynamometer during the smog test. When your car's tires are wet there is greater chance of slipping and losing traction as the smog technician tries to maintain required test speeds while on the dynamometer. Unstable engine and drivetrain torque is not the best conditioning your vehicle should receive if you plan on getting passing emissions test results. This is not to say you can't get a passing emissions test on a rainy day, certainly not. The smog machine has a "dry tires" mode, which will dry your car's, truck's, SUV's, or van's tires before the test. However as we mentioned, you don't want to place any extra strain on the engine before or during the emissions test.