As techs, we prefer to deal with the car with a driveability issue attached, as opposed to the light being the only problem, but both scenarios should be approached in the same manner.

Attach your scanner and make note of the codes that are recovered as you develop the diagnostic strategy for this job. But don’t be too quick to clear the codes; the next step is to review the freeze-frame data to see what was going on when the code was set. This information will be more helpful with certain codes, but it’s a good habit to get into no matter what the situation.

DRIVEABILITY ISSUES
First, we’ll look at some problems that have driveability complaints attached. The most common of these are misfire codes. If the misfire is obvious, you may be tempted to get to work and start switching coils, checking wires or whatever, looking to diagnose the problem. But before you do, check the codes and see if there isn’t more information available; if nothing else, the P0300 series of codes will identify the cylinder causing the problem.

But there are many other clues that may be available that will help in the diagnostic process. If you have a misfire code along with a system lean code, you should be thinking that the misfire could be a result of a manifold or other vacuum leak.

Even with no code, take a look at the data with an eye toward the fuel trim numbers: Do we have a high positive number on long-term trim, indicating th...

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