Before you start, always check the type of grounding system the vehicle has. If you remove the positive connector first in a negative ground system, you risk the chance of creating a spark. That could happen if the metal tool you’re using to remove the positive terminal connector comes in contact with any piece of metal on the car. If you are working near the battery when this occurs, it might create an ignition source that could cause the battery to explode. It’s extremely important to remove the ground source first.
Before you vehicle is scheduled for an emissions test it is a good idea to have your vehicle serviced and tuned up. Contaminated oil, fouled spark plugs and worn ignition wires can all contribute to an increase in emissions.
It is a good idea to go by your manufacturer’s maintenance schedule when determining how often to have your oil changed. If you have an older vehicle and do not have a maintenance schedule as a reference, a good rule of thumb is to have your oil changed every 5,000kms or every 3 months.