Understanding Your Smog Report

Understanding your car's smog report can be a little confusing even for the do-it yourself kind of guy or gal; however, here a few simple guidelines to help you with this, should you choose to do the repairs yourself.

I will also list some basic things to check for as it relates to your smog report. Due to the nature of how each vehicles make and model is made, some of this information may or may not apply to your particular case. Also, this is assuming you have a decent understanding of your car's system.

To begin with you have 5 readings to look at:

• HC-Hydrocarbons-Read in PPM(parts per million)
• CO-Carbon Monoxide-Read as a percentage
• 02-Oxygen-Read as a percentage
• CO2-Carbon Dioxide-Read as a percentage
• NO-Nitrogen Oxide or NOX-Read in PPM(parts per million)

Assuming you took your car straight to the test only station only to discover your car has failed, here some things to check for as it relates to your smog report.

In my experience high HC's can be an indication of bad spark plug wires, spark plugs, slow O2 sensor, or dirty air filter. A high reading is probably a good indication of unburned fuel. This will also affect your NOx readings as well.

High CO readings can also be caused by a faulty ignition system, dirty air filter, throttle body full of carbon and is a result of raw fuel passing through your cars system. A leaky fuel injector or cold start valve can also be the cause.

A high O2 reading can be the result of your car running lean due to the air/fuel mixture not mixing up properly.

Last and certainly not the least, is your NO or NOx reading. A high reading here usually has its roots with your cars EGR(Exhaust Gas Recirculation) system and catalytic converter. Things to check for in your EGR system; a sticking valve, leaking EGR valve, base gasket air leak, and carbon build in the passageway.

Things To Check Before Your Smog Test

For all you shade tree mechanics out there, here a few things to check for prior to that dreaded smog test. Now, assuming your car is in decent shape and you feel your car has a good chance of passing the smog test, here's what I recommend:

1. If your wallet permits, have pre-test done to give you an idea of your cars condition.

2. If you choose to skip the pre-test, then I highly recommend a compression test on your vehicle's cylinders.

3. With all the spark plugs out, examine your plugs and compare them to the images found on most car manuals, like Chiltons or Haynes publication. Here you'll get a decent idea on whether your car is running rich or leaking oil.

4. Check your spark plug wires, and valve gasket for any leaks. If your vehicle's manual recommends a valve adjustment, do it. Also, don't forget to examine your distributor cap and rotor or DIS system.

5. Check your air filter, EGR system, and throttle body for any carbon build up.

6. Check your cars exhaust system, including your catalyitic converter and play close attention for any defects. If you have a pyrometer or infrared gun available, check the temperature of the pipe entering the cat and compare with the temperature of outlet pipe.

7. Check your charcoal canister for any leaks or cracks.

8. Check all vacuum hoses and do the wiggle test on your cars electrical system.

So there you have it. I'm sure there are other things to check for, but those are some of the basics. Of course, be sure to replace all defective parts with new ones, or you can head to your local wrecking yard if your on a budget.

One thing I highly recommend is saving up for your smog test in advance, before that letter from DMV sneaks up on you. This way you avoid using that credit card.