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Q: Check Engine Light is on - 2003 Honda Accord

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The check engine light is on. This is the second time. I had it cleared the first time. Both times I noticed that it went on after I turned on A/C and same time turned to heat to defrost the window. The window is easily get foggy inside even on a not so wet day. I did some research online and I think the symptom is somewhat matches with that of the vacuum leak. My car is always jerky when I push the gas pedal, but it's still very powerful and no problem with accelerating at any speed. I can hear a hissing sound when I touch on the accelerating pedal. Could you help me to diagnose it? When I drove it to mechanics, they told me it's the Catalytic converter failed which I am not convinced because it is not matching the symptom of a failing catalytic converter. Thanks. Cindy

My car has 170000 miles.
My car has an automatic transmission.

A: Hello. If the issues appeared when using th...

Hello. If the issues appeared when using the AC and defroster, then they are likely related to that system. In most cases, the AC / Heater does not use vacuum lines as a part of it’s operation, so a vacuum leak is not a likely a cause for your symptoms. However, there are some exceptions. There are also a wide variety of issues that can produce the exact same symptoms as a vacuum leak.

If you believe you do have one, however, I would closely inspect the engine for any worn or damaged hoses and listen for any hissing sounds that may hint as to where the leak is coming from.

Finally, it may be possible that the catalytic converter is part of the issue, again though, this is less likely due to the fact that the catalytic converter and emissions system usually functions completely independently of the AC system. In order to give more insight on whether or not the catalytic converter is a part of the issue, this would require the trouble codes that came on when the check engine light came on. If you would like to get a more definitive diagnosis, a certified professional from YourMechanic can come to your car’s location to pinpoint the cause of the Check Engine Light and proceed with the proper repairs.

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