When testing my car's emissions, what does a "not ready" result mean?

Carmen’s Question: "I'm hearing a lot about vehicles failing their emissions test for "not ready" issues, can you explain what that means and how it can be fixed? My vehicle is a 1999 Pontiac Grand Am.”"

That’s a great question, and one that is becoming more and more common over the past few years.

First, let’s take a minute to understand just what is involved in vehicle emission testing here in Arizona. Older cars are tested under a standard called IM 147. IM 147 is the enhanced test used for most 1981 through 1995 gasoline-powered vehicles in the metro Phoenix inspection program. In this test, the vehicle is driven on rollers (called a dynamometer) at varying speeds to simulate urban driving. The exhaust is continuously measured and the results are shown in grams per mile.

On newer cars, an On Board Diagnostics (OBD) test is used. In this type of test, used on 1996 and newer light duty vehicles, engine operating data is accessed by connecting directly to a computer in the vehicle that continuously monitors engine emission control systems operation. The on-board diagnostic test does not measure tailpipe emissions.

One of the challenges encountered with this type of test is that the cars computer must be in “ready” status before the test can be completed. These computers on most cars will be in “ready” status when you arrive at the test center, but not always. If your car fails for a “not ready” condition, the most common cure for this is driving. Lots of driving. You should drive the car under various conditions; both freeway and city for a couple of days before returning to have it retested. Then on the day you’re going to take it back, make sure to drive at least 20-25 minutes at various speeds before pulling into the test facility. When you get in line at the test center, don’t shut the engine off as this may cause some of the readiness flags to reset to not ready status and then you’ll have to start all over again.

If you still have a readiness problem after following this advice, then you may want to contact your AAA Approved Auto Repair facility to have the car checked out or to receive more specific and detailed instructions for your particular model.