Auto Manifesto

May 18, 2009

OBD II Diagnostics

A few weeks ago the check engine light in my Mom's car came on, which was unusual. It's a 2004 Toyota Corolla with less than 100k miles. My Mom has had 3 of these cars over the past 20-some years; they last forever and are extremely reliable.

This model, though, has been less than stellar. It hasn't been unreliable, but there are a number of noticeable flaws relating to the design and materials. But I digress.

Anyway, there were no noticeable problems with the car's performance, and the engine light went off by itself within a few days, before she could get it to a service shop.

So I borrowed a colleague's OBD II diagnostic tool (by Innova; see and plugged it in to see if any problem codes were recorded. OBD II has been required by the EPA on all U.S. market light vehicles since 1996. There's a basic group of error codes required for emissions purposes. Then each vehicle manufacturer can also include its own codes beyond that for additional diagnosis.

In this instance 3 generic codes were saved, all pertaining to the fuel system. Prior to this I had already checked if the gas cap was on tight. If the seal is not tight it could also trigger the light. It's also possible that the seal is no longer effective but I suspect that the error codes were false signals. So I cleared them from memory and will revisit the issue if it pops up again.

Got to experiment, learned some new things and saved my Mom some money. This is pretty neat stuff.

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