Can I get my check engine light diagnosed for free?

The question I would ask is would you trust someone who would do it for free or should you? Today’s vehicles are complex electronic technical machines that have nothing in common with our parent’s cars in terms of operating systems. That said let’s look at a couple of scenarios we’ve run across several times over the years.

Scenario 1: I just took my car to x-brand auto parts store and they scanned my check engine light for free and they said it was the oxygen sensor. I replaced the part but the light came back on. Where did you buy the part? The guy that scanned the car sold it to me. Hmm… how much time did he spend actually diagnosing the problem? Well, only a minute, he just read the code.

You see this is somewhat similar to going to the pharmacy and asking the person at the counter to diagnose your chest pains based on your symptoms. He grabs a stethoscope and listens to your heart and says yeah you need a transplant. We just happen to sell new ones here! I know a bit of sarcasm there but you get the idea.

Scenario 2: I just took my car to x quick lube and they read my car’s check engine light code and said I need a new oxygen sensor. Can you put it in for me? Maybe, which sensor? The oxygen sensor. No I mean which oxygen sensor, your car has 4 of them, 2 pre-cat and 2 post-cat. Oh I’m not sure he didn’t say.

Most reputable shops today invest a substantial amount in training for their technicians and as much or more in the diagnostic equipment needed to properly diagnose your check engine light. Reading a code from a scanner is not the same thing. The oxygen sensor code flagged in the afore mentioned scenarios only indicates that the engine management processor is “seeing” a sensor that is sending back a reference signal that is out of the parameters that the engineers coded into the program. What a good technician has to do is determine why that signal is out of line, and that could be due to a whole host of possibilities.

Next time you find yourself with that pesky check engine light on rely on your service professional, it will save you time and money.