Well, full tank or not, the minivan does not pass muster.
Now what? This Instructable will help you use scan tools to diagnose your car's problems. You can do the basics yourself before taking the car in to a mechanic.
This project was originally published in the August 2001 issue of Popular Mechanics. You can find more great projects at Popular Mechanics DIY Central.
Step 1: Use an OBD II
on the Check Engine light like you can on earlier computer-controlled vehicles. You could take your minivan into a high-tech shop, where the minimum charge for diagnosis and inspection could run you somewhere into three figures. Or you
can learn about OBD II yourself, but you will need a piece of diagnostic equipment that you probably don’t have—an OBD II scan tool.
If the Check Engine light came on, it should be no surprise that the vehicle failed an emissions test. With OBD II, that light comes on only if there’s a failure that significantly affects emissions. That makes the scan tool even more important since it will reveal a lot of the problems that do not cause the warning light to come on.
With many problems, the light stays on after the repair is made and the code remains in the computer memory for a certain number of ignition on/off cycles. Your daughter didn’t tighten the gas cap correctly, causing a code for the evaporative emissions system to set. Eventually the light will go out and the code will self-erase, perhaps after the next time you start and stop the car. You also can use the scan tool to erase it immediately.
With many other problems, however, the only way to turn off the light and erase the code is with the scan tool. Just a warning: If you erase trouble codes with a scan tool or disconnect the battery for any reason, you also erase the computer’s continuous monitoring system. So if you take your car in for a state inspection before enough normal driving, the computer might not have completed all its tests, and your car will fail inspection for that reason.
The OBD II scan tester not only will enable you to find answers to the simpler problems, but will tell you into what areas the seemingly more complicated ones fall. Then you will have a better understanding of what the technician is (or should be) looking for.