Are Lights the Only Thing the OBD Uses to Warn the Driver of Issues? | YourMechanic Advice

Are Lights the Only Thing the OBD Uses to Warn the Driver of Issues?

If your car was manufactured after 1996, it has an OBD II system that monitors emissions and other systems on board. While it’s primarily focused on emissions, it can also report other problems that are only peripherally related to emissions (engine misfires, for instance). It communicates any potential problems to the driver through a single light in the dash – the Check Engine Light, also called the MIL or Malfunction Indicator Lamp.

Is the Check Engine Light the only connected light?

Yes. The only way your OBD system has to communicate with you is through the Check Engine Light. What’s more, the other lights in your dash are NOT connected to the OBD system (although advanced scan tools can access the car’s computer and read many of these trouble codes via the OBD II connector under the dash).

Common reasons the Check Engine Light is illuminated

If your Check Engine Light flashes on right after the engine cranks, and then turns off again, this is normal. This is the self-check procedure, and the OBD system letting you know that it’s operating.

If the Check Engine Light comes on and stays on, it means that the computer has identified a problem that has some sort of impact on emissions or engine control. These can range from engine misfires to failed oxygen sensors, dead catalytic converters and even a loose gas cap. You’ll need to have the code pulled by a mechanic to begin the diagnostic process and determine the cause of the problem.

If the Check Engine Light comes on and begins flashing, it means that your engine may be experiencing significant misfires, and that the catalytic converter could overheat as a result, causing a fire. You should immediately stop the car and have a mechanic diagnose and repair the problem.

While the OBD system can only use the Check Engine Light to communicate with you, it’s vital that you pay attention to that light and know what to do.

Next Step

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21 years of experience
196 reviews
21 years of experience
BMW 330Ci - Check Engine Light is on Inspection - Little Elm, Texas
Edmar was friendly and knowledgeable. He took the time to explain upcoming maintenance items and which ones could be done together to save on labor costs and time.
Cadillac CTS - Check Engine Light is on - McKinney, Texas
Edmar is always professional and he knows his craft. He never dissapoints. He is my go to Mechanic.


25 years of experience
7 reviews
25 years of experience
Chrysler Town & Country - Check Engine Light is on - Romulus, Michigan
Very professional! On time, went right to work. Explained what was done & what would be needed. Compete clean up of area when he was done.
Ford Fusion - Check Engine Light is on - Ann Arbor, Michigan
Mike was very thorough with his work and explained everything that was recommended for safe operation of my vehicle. He went out of his way to do the job well.


17 years of experience
47 reviews
17 years of experience
Nissan Sentra - Check Engine Light is on - Greensboro, North Carolina
He was very professional and gave me a lot of insight on the problem with my car. I would definitely recommend him to my family and friends
Infiniti FX45 - Check Engine Light is on - Greensboro, North Carolina
Very knowledgeable and gave me a detailed description of the issue. Will continue using him anytime he’s available.


16 years of experience
216 reviews
16 years of experience
GMC C1500 - Check Engine Light is on - San Antonio, Texas
Gustavo was on time exactly. He called me to let me know he was on the way. Repaired the items on my quote. He diagnosed the rest of the Truck on his 50 Pont inspection. Showed us the little things we needed to address. Shortly my 1990 GMC will be working great again. He's fantastic, I'll use him again.
Ford F-150 - Check Engine Light is on - San Antonio, Texas
As a woman, I trust what Gustavo tells me. Last appointment, he went to my home for the repair and this time, he came to my work. Gustavo explains everything to me in a manner I can understand and takes time to answer all my questions. I won't use anyone else.

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