You’ve probably seen the ads on TV: The local auto parts store will be happy to check your car’s codes for free, and sell you the parts you need to fix it yourself.

Sounds almost too good to be true. And it is.

Oh, sure, they’ll check the codes. They have the scan tools to do that. And they’ll tell you what the code says and sell you the parts that those codes indicate. But here’s where that gets a little sticky: Those codes don’t guaranteed that you need the part.

That’s because a code indicates a sensor that’s varying outside the norm. Could that be because the part is faulty? Sure. But it could also be because another part failed: one that has nothing to do with the code. A problem with one sensor circuit can set codes for other sensors, simply because they share the same power or ground source. You end up buying unnecessary parts, wasting time, and getting nowhere.

That’s why it’s usually smarter to bring your car to a qualified technician when your “check engine” light comes on. They have a clearer understanding of the systems involved and are more likely to be able to trace circuit problems back to their original source. The technicians at your local Cottman Transmission and Total Car Care center have the education and equipment to analyze your car’s computer system, and are more likely to address the root cause of the problem, rather than throw parts at it in the hopes of hitting the right one.

Maybe all you need is a simple sensor replacement. In that case, their technicians will replace that sensor, clear the codes, and keep track of the repairs they performed. If something else shows up, they’ll have your history to refer to, and are more likely to isolate any additional problems, without revisiting the same repairs. That saves you time and money.

So, yes, the local parts store will be happy to check your car for codes and sell you parts. But for a proper diagnosis, always bring your car to a qualified technician, like the technicians at your local Cottman center.