How does the Check Engine Light feature work?

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Posted 2 years ago

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When does the check engine light turn on?
The check engine light comes on when the vehicle’s engine control unit (ECU) detects a problem that may affect vehicle performance and emissions.

How do I know what’s wrong?
The engine control unit reports diagnostic trouble code (DTC) that describe the issue detected. Automatic can read these trouble codes and describe what they mean.

What do I do when an issue is detected?
If your engine is not stalling and drivability is not affected, you can try to fix the issue(s) and clear the check engine light yourself. Many websites and online user forums offer diagnoses and solutions for trouble codes. Be careful when following advice from unverified sources. Consult a mechanic if you’re not sure what to do.

What if my engine light is on, but there are no trouble codes?
Some trouble codes are proprietary to your vehicle’s manufacturer and might indicate a problem Automatic cannot detect. For a proper diagnosis, please take your vehicle to a mechanic who specializes in your vehicle’s make.

What does reseting the check engine light do?
The check engine light clears when Automatic resets the vehicle’s engine control unit (ECU). Resetting the ECU doesn’t resolve any underlying problem. If the problem persists, the light will turn back on.

Resetting the ECU doesn’t modify your vehicle’s computer system, but simply resets its diagnostic tests. This will temporarily alter your vehicle’s performance and make it temporarily ineligible for emissions tests.

How do I know if the problem is fixed?

It depends on the problem, but it may take 3-4 days of driving for your vehicle to perform the necessary tests and determine if the problem still exists.

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