Thursday, June 11, 2009

Check Engine Light Came On, Now What?

Ever been driving along and all of a sudden your check engine light comes on? Do you know what to do? "That's a silly question, we take it to a mechanic stupid!" I know, I know, so do a LOT of people, and then you lose hundreds of dollars out of your wallet for "diagnostics". And the funny part is, if you have a CEL your car is already telling you what the problem is!

All post 96 year model cars are equipped with a universal "language" if you will called OBD2 (On Board Diagnostics). This "language" uses a set of universally understood numerical codes that are associated with your cars vital systems. A CEL on the dash simply means one or more of your car's systems has exceeded a threshhold set forth by the manufacturer and it is no longer functioning properly. For instance, a P0304 code means you have a misfire on cylinder #4. A P0128 code means your thermostat is running cooler than it should and so forth. You can find a link to all the codes here: (note: there are also manufacturer specific codes too, which I will deal with later, keep reading).

So now that you know that, what now? Surely you have to spend a ton of money to get a certified mechanic to read the codes on his million dollar computer right? WRONG! General OBD2 scanners can be purchased from $39 up to $109 depending on features and style (you can even obtain BMW specific code readers for $100-$150). Your local auto parts store (AutoZone, Advance, Oreilley) will even read the codes for you at no charge!

Here are a few reasons why having a list of the codes is so important (even if you aren't a mechanic or going to try and do the work yourself):

1. Knowledge is power. If your car is throwing a thermostat code, and the mechanic says you need a new muffler, you can politely tell him how he can cram the muffler up his.......
2. You can determine the severity of the problem. If you are like me, sometimes money isn't falling out of your pockets. And if the code is a non critcial code (like an 02 sesnor code) then you know that you can still drive your car without risking major damage until you can afford to have it repaired.
3. You can post the codes on online forums and get an idea of what needs to be done, costs associated, and helpful tips. A lot of car specific forums (like Bimmerfest) have people on them that know a TON about the problems and issues with a specific car. They will often give you free tips and tricks to help.

So you see, the CEL is nothing to fear. Sure, sometimes your CEL can be something serious. But more often than not it is simply something you have neglected to replace because hey, you have a life right?

The next time your CEL pops up, head over to your local auto parts retailer and have them pull the codes and do some online research. You might save yourself $100's of dollars or more!


  1. Hi, great post.
    I own a BMW 323i and lately a light named EML came up and I have no idea what it is, I took it to a mechanic and he said I needed to pay 2,400dls for repairs of a bunch of stuff. I wanted a second opinion so I was looking around and found your blog now Im going to Autozone today to check the codes. Im surprised Autozone also has the free code reading service here in Mexico, already called them up to verify it.
    Thanks for the great tip.

  2. That is awesome! I had no idea that you could take your car to an auto parts store and get the codes read. The dealer charges an arm and a leg. Put that in your Bavarian pipe and smoke it Mr. service writer..

  3. Very inspiring. I have enjoyed reading your blog & it is both instructional & interesting.
    San Jose Auto Repair