Q: The car shakes during braking and at stop lights, error code P0420

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Recently, the code P0420 came on. I have problems with my car vibrating at the stop light when I'm braking. It starts running normally again when it is in neutral or when I speed up. There are no changes in fuel economy. I think this shaking has to do with the error code. It indicates issues with a possible leak, the catalytic converter, sensors. Please give me some advice on what to do as I would like to know more about this code and my car shaking. Thank you in advance.

Hi there. The P0420 code you are getting can cause your car to run like this. The code typically means that the catalytic converter is failing or one of the oxygen sensors may be failing.

If it was the converter, then you would typically have a loss of fuel mileage and engine power. If you do not have those, then it may be a sensor. I typically start by installing a scan tool and monitoring the oxygen sensor signals as that will let me know if the sensors are failing. If you plan on having this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose and repair your car’s Check Engine Light and shaking issue.

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