The Basics of Check Engine Lights, Part I

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Mint Hill, NC – Last week, we talked a bit about what check engine lights are and what they can do. Today, we’ll talk about what they can’t do.

A lot of times I’ll get asked “is pulling a Check Engine Light Code diagnostic?” and the answer to that is no. Codes, while great for pointing you in the right direction, are not diagnostic. Example: Let’s say your check engine light comes on and it’s a P0456 – Small EVAP Leak Detected. Simple right? Not quite. EVAP is short for an evaporative emissions system. This system has lots of different parts involved. The charcoal canister, canister vent valve, purge solenoid, purge valve, vapor lines, and your fuel tank are just some of the parts EVAP systems. Did that code tell us which of these things went bad? What if nothing is bad at all, and your vehicle’s computer (PCM) isn’t testing correctly causing a false-positive?



We don’t know, and we can’t until we dig a little deeper. That is diagnostic. Codes are helpful, they steer us in the right direction, but they aren’t genies in a bottle.

Remember, OBDII was implemented in 1995 and hasn’t changed much. Do you have a smartphone, or a fairly new Mac, or a Windows 10 PC? You know what those are capable of, right? Well, your car is running the automotive equivalent of Windows 95. While there is better tech out there, it hasn’t been federally mandated yet. So until that day comes, OBDII is the path we’re going to take.

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