Troubleshoot the Check Engine Light Yourself and know Your Mechanics Dirty Little Secret


Even if you find a good mechanic, if you’re like me, you shiver at the thought of paying hundreds of dollars for major vehicle repairs. Even more, you dread paying $100 just to have your mechanic take a peek at your vehicle to tell you that nothing is wrong with it – but that’s what you get for being a responsible auto-owner. Or is it?

There is an alternative to those annoying ‘take a peek at it’ vehicle labor expenses. And it costs nothing. The service engine light comes on in your vehicle because the computer has diagnosed that something ain’t quite right. When the light comes on, a code is stored as the reason for triggering the light. When you take your car in to get it checked out, the mechanic hooks up a little diagnostic computer to your vehicle’s computer. They will then get a code and description that tells them what the issue is.

OBD-II: A Background on Auto Diagnostic Codes

Every vehicle recently sold in the United States has an onboard diagnostic system that self-diagnoses a variety of vehicle issues through the vehicle’s diagnostic computer. The connector to this diagnostic system is called OBD-II (on-board diagnostic, version 2) and it is standardized for every vehicle sold in the US, 1996 and newer. When your on-board computer detects a problem, it outputs a code through the output, and the code can be read by an OBD-II code scanner, or reader.

OBD-II codes, or PID’s can help diagnose powertrain, emission, and other vehicle issues when diagnostic readings are out of accepted ranges. You can find a list of OBD-II PID’s here.

Check Engine Light: The Mechanics Dirty Little Secret

What your mechanic probably won’t tell you is that you really didn’t need to shell out $100 just for them to hook up an OBD-II scanner to check on the service engine light. You can get that for free at most auto-parts stores. I’ve had this done at Napa and Advance Auto Parts. It costs nothing. The auto part stores carry these to cater to DIY’ers in hopes that they, in turn, buy the auto parts at their store to make the fix on their own. It takes them 1 minute to do this.

I was relieved to find out that the cause for the light to go on in my car was a possible vapor leak coming from my gas cap, caused by a weak spring in the cap. The gas cap costs $10. The store can also reset the computer so that if the problem persists, the light will come on again. If it doesn’t, problem fixed.

There probably are some honest mechanics out there who won’t charge you for this. But good luck finding one (perhaps, asking if they offer a free check engine light scan and their response is a good measuring stick for an honest mechanic).

Get your Own OBD-II Scanner

If you want to take things yet a step further and not go to the auto parts store every time, you can purchase your own OBD-II scanner. Here’s a very well rated OBD-II scanner for just $17. And there’s a bluetooth-enabled OBD-II scanner for just $22. That’s one-fifth what mechanics will charge for JUST ONE CHECK! Both of these scanners will give you a description/meaning, along with the actual code number. Very easy.

Oh – another thing – replace your car’s air filter on your own – it’s easy, and will save you a lot of money versus having a mechanic do it.

Check Engine Light Discussion:

  • What clever techniques have you used to avoid vehicle service fees?
  • How much were you charged to have your car ‘looked at’?