Your vehicle is equipped with a sophisticated On-Board Diagnostic (OBD) system. This is what has turned on your Check Engine light, or MIL (Malfunction Indicator Lamp).
We are well-equipped and trained, so that in most cases, we will be able to diagnose and repair problems quickly and accurately. However, there may be more than one problem present, even though only one ”code” appears in your computer.
The OBD system performs a series of ”self-tests” to determine whether all systems are working as designed. Once a failure occurs, many of these tests are temporarily turned off. This means that once we fix the problem that caused the original code to set, we may discover other problems that could not be detected until the first problem was solved. This is especially likely if you have been driving with the Check Engine light (MIL) on for more than a few days.
Some of the self-tests require certain specific conditions to occur before they can be run. Some, for example, may require that the engine not be started for at least eight hours since the last trip, and that when it is started, the outside temperature must be warmer than 15°F. Others require that the fuel tank be between one-half and three-quarters full. Most require that the vehicle be driven for several minutes at a steady speed of more than 50 MPH. There are many other requirements for each self-test, and all must be met before those tests can be run. Additionally some tests must be run more than once before they will register a failure.
It would not be practical for us to have to keep your car and drive it so extensively. That’s why we must rely on you to do your part. Each of the OBD self-tests will run eventually during normal driving. You will need to bring your vehicle back for further repairs if the MIL illuminates.
When you pick your car up after it has been repaired, you will be given a form that lists the specific codes present in your computer at this time. That way, you can have confidence that any future problems are not related to the same cause.