The check engine light in the mobile net era

We're on day two of a two week family road trip and our 2000 Mazda MPV Van check engine light comes on.

On a Sunday.

Once upon a time, this might have led to an urgent search for an open garage.

Ahh, but now we have and iPhone and, at least until we hit Canada, net access.

So instead of pulling over, Emily researched and I drove. We found out ...

• This should really be called the check emission control system light. In most vehicles it's triggered by a sensor in the emission side of the engine.
• The most common cause is a loose gas cap. Presumably the loss of suction causes venting of gas into the emission systems.
• Rarely it can be something bad with the engine, so the official word is always to get it checked out. If you play the odds though ...
• Depending on the car it can cost $150 or more to read off the error code (my next car needs to have a diagnostic USB port on the dash as well as 4 110 V outlets - it's insane these are so hard to read).
• In some cars the light won't ever go off until the dealer checks it out. In others, if the problem is corrected the light will eventually go off. The trick is that this may take 15-20 restarts (the number of restarts seems to be more important than time, presumably due to how the sensor works.

Emily had already noted that I'd only turned the cap 'one click'. (Ok, so it wasn't all iPhone. She remembered some of this stuff.) So simple Bayesian reasoning (prior probability, etc) meant there was a very high probability this was a (stupid) gas cap alarm.

So we just drove.

We stop and start a lot on our family trips, so about 3 days later we' d hit about 15-20 restarts and ...

The light went out.

We sacrificed a GB to Google in gratitude.