Q: P0420 motor mounts on a Hummer H3?

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I have a 2008 Hummer H3 that is throwing P0420. I decided to take it to a dealer because I also needed the a/c recall work done. THey diagnoses the problem as motor mounts and quoted a high price for repair. Is that a possibility or was I lied to? I don’t want to chase something if that’s what it is. But I fail to see how motor mounts could mimic an O2 sensor or cat converter.

My car has 136000 miles.
My car has an automatic transmission.

Hi Jimmy. Thanks for contacting us today. I’m in agreement with you - in that the replacement of engine mounts is NOT a solution to resolve a P-0420 Error Code. You should read this article about this code - to review possible causes and repair options. What is likely is that Hummer dealer completed a (100-point inspection) along with the scan and determined that the motor mounts were damaged and required replacement. It’s also possible that they never resolved the error code. I’d ask them to explain how motor mounts are related to this code - as we’d be curious to see this explanation as well.

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