Thing I Learned: Check Your Damn Gas Cap!

Yikes! Scary light!

After a long trip, the dashboard of our Scion xD lit up like a Non-Denominational Gift Giving Holiday Display.


Since this is our “good” car (in contrast to¬†our Prius with the bum AC, which is miserable for summer¬†road trips), I high-tailed it to the mechanic, terrified that we’d done Something Bad to the car that we’re relying to get us through at least another two years (at which time our youngest can enroll in public school, freeing up $1200/month for an auto payment on something big enough for us all to not drive each other to the brink of murder¬†during every damn road trip).


  1. Our mechanic (Rons’s Garage, God-of-yr-Choosing¬†bless ’em!) is fantastically honest and
  2. It was nothing

So why the light display?

We’d left the gas cap off.

We fueled up as we rolled back into town, as my wife needed the car for work the next day (a ~30 mile drive). ¬†And we hadn’t screwed the cap down all the way. ¬†A loose cap¬†makes the car’s computer¬†believe there’s an air leak somewhere in the fuel system (’cause there is–around the lose cap. If you’re wondering why the car gives a damn:¬†To ruy efficiently, you need to¬†maintain a proper fuel-air ratio in the engine, and it’s easiest to control this if you have a sealed fuel system. ¬†On top of that, petrol fumes are bad news for the environment, so many car’s¬†additionally check for leaks just to make sure you aren’t wrecking up the joint¬†with stray hydrocarbons).

The car can run basically fine like this, and there’s no real danger of damaging the engine. ¬†Put the fuel cap back on, reset the warning light, and all is well.

The lesson: ¬†If your car is throwing a CHECK ENGINE light, make sure the gas cap is tight. ¬†If it’s loose (or you lost it), then tighten it down (or replace it), and keep driving. ¬†If there’s nothing obvious wrong (no sluggishness or weird noises) and it isn’t nearly time for an oil change, you’ll be fine, and the light will reset itself within 100 miles. ¬†If it stays¬†on, then go to the mechanic.

Ron didn’t charge me, because he’s a solid dude¬†(which is why I keep going there). ¬†But plenty of guys would charge you for figuring it out (they did spend time pulling the code from the car’s computer and troubleshooting my dumbassery), and a few¬†would even use¬†this¬†as an excuse to “repair” some “major problem.”