Except for ensuring proper engine temperature, a smog technician can not and is not allowed to refuse inspection of a vehicle based on knowing the vehicle will not pass the emissions test due to any pre-existing circumstance/s, whether those be an illuminated check engine light, disconnect vacuum hoses, missing smog components, or any other emissions failure which will stop a vehicle from passing the test.
The emissions technician must perform the emissions test and not pass the vehicle. This is part of California's State Emission Laws. You may want to ask for a pretest. All smog stations offer this service usually for a small fee; much less then the actual cost of the complete emissions test.
The 8 Tips that Will Help You Pass the Emissions Test
To be observed: Before arriving to the emissions test center.
1. Running Right - Do not get an emissions test if you suspect your vehicle is not driving, running or functioning properly. Consider this, many vehicle's do not pass the emissions test although their owners never suspected any problems. They're simply shocked when they find out. Now, if your vehicle is already experiencing obvious problems, don't waste time or money on a smog check. More than likely it will not pass the emissions test and you will lose your inspection fee. Seek repair assistance first. This will ensure your vehicle passes the emissions test the first time. Plan ahead.
2. Check Engine Light Off - Check engine light should not be on. As discussed in our functional test page, an illuminated check engine light will cause your vehicle to not pass the emissions test automatically. A certified emissions repair shop can use a trouble code retrieval tool to extract trouble code data from the ECU and perform necessary repairs to turn the check engine light off.
3. 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. Ensuring your vehicle's tire pressures are even and correct will help you pass the emissions test. Correct tire pressure will allow the vehicle to be driven with greater stability and control during the emissions test. This will greatly improve your chances of passing the emission test by allowing the engine to maintain a constant and steady load. Accurate tire pressure (as required by the tire and vehicle manufacturer) may be the deciding factor between a borderline vehicle passing or not passing the emissions test. 2000 and newer vehicles are not administered the exhaust emissions portion of the smog test. This passing tip, as well as tips number 5 and 7 don't really 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.
4. Change Engine Oil - If you haven't performed an oil change within the last 5,000 miles, go ahead and do it before the emissions test. This will assist in getting passing emission test results. Your vehicle's Positive Crank Ventilation (PCV) system is designed to allow the engine to breath fumes from the oil compartments. 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 emissions test. Contaminated oils are high in Hydrocarbons (HC) and will present a rich mixture to the combustion chambers. Not performing regularly required oil and filter changes not only causes premature engine wear but can also cause your vehicle to not pass the emissions inspection.
5. Take a Drive - Drive your vehicle for at least 20 minutes prior to arriving at the smog station. This will ensure your coolant, oil, and catalytic converter reach and maintain optimum operating temperature. This will help your vehicle pass the emissions test as well. Remember your engine is a fuel burning machine. To ensure a passing emissions test and adequate combustion it needs to have sufficient time to warm-up and this can be accomplished through driving for at least 10 to 15 miles. Emission test standards require a smog check technician to ensure a vehicle is at proper operating temperatures prior to administering the emissions test, however this is one conditioning that will help pass the emissions test which you can perform as well.
6. Use Fuel Additives - 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 with your 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.
7. Avoid Wet Weather - Try to pick a nice day to have your vehicle tested. This will help your car pass the emissions test. Avoid the rain. Let us point out a few problems with rainy days. Your vehicle (assuming it's registered in one of the larger counties in California and is model year 1999 or older) will need to be driven on a dynamometer during the emissions test. Obviously when wet, your car's tires will be slipping and losing traction as the smog technician tries to maintain required test speeds. Unstable engine and drivetrain torque is not the best conditioning your vehicle should receive if you plan on getting passing emissions test results. You want your vehicle's engine running super comfortable, not high stress. 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 vehicle'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.
8. Battery Recently Disconnected? - If your vehicle's battery has recently been disconnected due to it having needed replacement or battery charging, or if your vehicle recently needed a jump start, we recommend holding off on getting the smog check for at least one week while you drive your vehicle regularly. Chances are while your vehicle's computer lost power, its internal self test monitors were erased. Without these important and 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 in order to reset or "complete" the emission monitors. This period of driving is referred to as a "Drive Cycle".
Additional Advice on Passing The Emissions Test
To be observed:
During the emissions test at the smog station.
1. Proper Vehicle Description - Passing the emissions test requires correct input of your vehicle's year, make, model, engine size, and GVWR weight. This information is required by the smog machine in order to calibrate dynamometer load, and set proper RPM to MPH ratio designed specifically for your vehicle by the California Air Resources Board. You should ensure the smog technician is well aware of all your vehicle's details, i.e. custom components, engine changes, out-of-state vehicle, so on. Improper or inaccurate settings entered into the smog machine will produce significantly different emissions results, effecting your chances of passing the emissions test.
2. Properly Trained Technician - You need to ensure your emissions technician is properly trained. This does not require you hold an emissions test license as well. Just look for simple signs. For the most part the emissions technician will be entering data into the smog machine and you will not be able to view his or her entries. But what you may want to observe is how the emissions technician mounts your vehicle on the dynamometer, how quickly he or she is able to locate proper emissions components, and how well they are able to maintain required driving speed during the dynamometer portion of the emissions test. Making sure that the technician drives your vehicle smoothly, applying gas and brakes evenly and only when required will make it more likely that you'll pass the test.
If your vehicle did not pass the emissions test and you feel it was due to an error on the smog technicians behalf, feel free to voice your opinion to the technician. Explain how you know that proper driving is pertinent to passing the emissions test. They may offer to test the vehicle again, or explain why they performed the emissions test as they did. Note: The dynamometer will test your vehicle at both 15mph and 25mph. The transition will be fast and the vehicle will be required to accelerate quickly during the test. Do not be alarmed.