Q: P0420 code and engine is not starting.

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Got the SES light on a few days ago. Checked for the OBD code, got a P0420. Continued driving, felt a little lack of power 2 days ago on the highway at 120 km/h.

Yesterday morning, when I tried to start it, the engine cranks up, but does not fire up. Battery is good, replaced a few months ago. Engine cranks normally, but shuts down with a cluttering sound.

Is there some engine damage, or the ignition/plugs are misfiring, which might have caused the P0420 in the first place?

Will a detailed diagnostic help?

Thanks.

My car has 115000 miles.
My car has an automatic transmission.

Hi there. The p0420 code means that the catalytic converter is below threshold and is not functioning correctly. This code comes up when the catalytic converter can no longer burn off any fuel in the exhaust system. Take a raytech gun (thermal gun) and check the temperature of the pipe before the catalytic converter and check the pipe after the catalytic converter. If the temperature is the same, then the catalytic converter is not working and would need replaced. If the temperature is 100 degree difference, then the down stream Oxygen sensor has failed. Either way, then computer sees this and has put the engine into limp mode and is making the engine run poorly and stop running. Since you are hearing a strange noise as the engine is not starting but cranking, the catalytic converter could be plugged up causing a restriction on the exhaust system. I recommend seeking out a professional, such as one from Your Mechanic, to help you diagnose your exhaust system.

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