My car’s check engine light on! What do I do?

Check engine light onSometimes the simplest explanation is the answer, but the solution becomes obvious only after the fact. My check engine light turned on last week, and I sort of panicked. My car was relatively new with a good maintenance schedule—why is it flipping error codes on me?

For most passenger vehicles built after 1996, on-board diagnostics (OBD2) is able to produce error codes that help you troubleshoot your vehicle. There is a serial port-like output often on the lower left side of the steering wheel where you can plug in the scanner. An OBD2 scanner can be purchased for less than $30 on for self-troubleshooting. If you go to your local AutoZone, O’Reillys, or your local dealer, they will have the device to scan your vehicle.

Common causes for check engine light include:

  • Gas cap loose – A loose gas cap on a modern vehicle will flip the check engine light. The gas tank belongs to a complex system that allows your car to remove and dispose of vapors in the tank. ACGO has a great overview of this system.
  • The oxygen sensor needs to be replaced. The sensor detects the amount of unburned oxygen in your exhaust. If it malfunctions, you can still drive your car, but the fuel economy will likely decrease.
  • Other items upstream of the oxygen sensor: spark plugs, air flow sensor, catalytic converter.
  • Evaporative vacuum hose leak.
  • Not so common: if you’re messing with your car alarm system or recently installed an aftermarket remote starter kit, you might want to check your wires.

In any case, most of these faulty devices will cost you hundreds (thousands if your dealer rips you off) to replace.

Fortunately for me, my fuel cap was loose:

Subaru gas cap
Tighten your gas cap or your check engine light will turn on!

The cap actually has printed instructions to tighten it!

If you have any questions or comments, sound out below! Any car problems to troubleshoot? Sound out below!

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