by Jim Kerr

While vehicle emission testing isn’t necessary in all provinces, some areas of the country such as British Columbia, Ontario, and New Brunswick do have mandatory testing programs. Eventually, testing will be introduced in other provinces and all cars and light duty trucks will have to pass or be pulled off the road. Even if you don’t currently live where vehicles are required to pass vehicle emissions tests, you may move to a province that does or you may wish to sell your vehicle to someone living in an emissions certified province. If you need to have your vehicle emissions certified, there are a few simple things you can do first to help your vehicle pass.

First, make sure all the emissions equipment is on your vehicle. The first part of an emissions inspection is to make sure all the emissions equipment is in place. Remember that your vehicle is only required to have the equipment it originally came with. The most common items that are missing or have been disabled are the EGR (exhaust gas recirculation valve), air pump, or heated air intake pipes.

The engine has to be running smoothly. Misfiring sparkplugs, vacuum leaks, or rich fuel mixtures will cause the vehicle to fail emissions testing. Even very dirty engine oil can cause a failure because the oil fumes are drawn into the engine and some may pass out the exhaust. Make sure the engine is operating at the proper temperature. A faulty thermostat can cause the engine to operate too cool and this in turn causes too much fuel to be injected. Again, you fail the emissions test.

Even if you think your vehicle is running fine, you should prepare it for emissions testing by taking it for a run on the highway. Depending upon your vehicle condition, this may take only a few minutes or it could take up to an hour. Driving at higher speeds tends to clean out sparkplugs, clear carbon off oxygen sensors, and burn residue out of the catalytic converter.

Immediately before the vehicle is tested, the emissions system must be “conditioned”. This is done by running the engine on a fast idle for up to 15 minutes. Conditioning the vehicle ensures the engine is at full warm operating temperature, the oxygen sensor is hot and sending signals, and that the catalytic converter is working.

Catalytic converters must be hot to work. The manufacturers try to keep the converter as close to the engine as possible so it will always be hot, but some body designs do not allow this. If the converter is back beneath the vehicle and if the engine has been idling at a slow idle for a few minutes, the converter will cool down and stop functioning properly.

During the emissions test, the technician will measure hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). HC (hydrocarbons) are mostly composed of unburned fuel. A misfiring cylinder will cause the HC levels to be high. CO is produced as a normal by-product of combustion but high levels can be controlled with careful fuel management and the use of a catalytic converter. If the fuel mixture going into the engine is on the rich side (too much fuel) then the CO levels will be high. Something as simple as a dirty air filter can also cause CO levels to be too high. NOx is created when combustion temperatures are high. It is often controlled by engine design, or the use of Exhaust Gas Recirculation (EGR) to lower cylinder temperatures, and the catalytic converter. Incorrect ignition timing can cause cylinder temperatures to rise and NOx emissions to skyrocket. So can a lean fuel mixture.

Most of the time a vehicle fails emissions testing it is because of simple things: bad sparkplugs or plug wires, dirty air filter, incorrect ignition timing, or a rich fuel mixture. Routine maintenance and a thorough pre-test warm-up will help your vehicle pass emissions tests. Passing an emissions test shouldn’t be a chore. When you pass, it means your vehicle is running properly, and with the high cost of gasoline, who wants to drive a vehicle that isn’t!

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist’s Association of Canada (AJAC).

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