Check Engine Light Diagnosis and Repair In Missoula.

The check engine light comes on when your vehicle's computer sees a problem with the engine, the emissions system, a sensor that monitors them or, on many vehicles, the transmission. It stores a trouble code describing which system or circuit is out of range. The light doesn't tell you how serious the problem is, and the code doesn't tell you which part failed. That's what diagnosis is for.

Pay attention to how the light is acting. A steady light means the computer found a fault and it should be checked soon. A flashing light usually means a misfire bad enough to damage the catalytic converter. If yours is flashing, ease off, avoid hard acceleration and get it checked before driving much farther.

The causes cover a lot of ground. Some are small, like a gas cap that isn't sealing or a sensor that's failing. Some are emissions faults, like a leak in the system that captures fuel vapor or a catalytic converter that isn't working efficiently. Others are mechanical, like misfires, vacuum leaks or a thermostat stuck open so the engine never fully warms up. Left alone, some of these hurt fuel economy and some lead to bigger damage.

That's why we don't just read the code and replace the part it names. We pull the codes and the freeze frame data that shows conditions when the fault was recorded, look at live sensor readings, and then test the specific circuit or component involved. An oxygen sensor code, for example, can be caused by the sensor, its wiring, an exhaust leak or an engine that's running too rich or too lean. Replacing the sensor without checking can leave you with the same light and less money.

Once we know the cause, you'll hear it in plain language: what's wrong, how urgent it is, what can wait and what each option costs before we start. If you've already been told you need a big repair because of a check engine light, we'll give you a free second opinion.

After the repair, the codes are cleared and the system is checked. Some emissions monitors need a stretch of normal driving to finish their self tests, so it's normal for a few to show as not ready for a little while.

If your light is on, call or schedule a visit and tell us anything you've noticed along with it, like rough running, a smell, a change in fuel economy or when it first came on.