Prius 2007 2gen hybrid help

P0420 is your catalyst below threshold meaning your catalytic converter is worn out or it doesn't meet the parameters for the computer to call it good I'm in a state where I don't have to pass emissions so this doesn't matter but the many and the rest of the country it matters very much generally you're going to be buying a Toyota converter putting it on the car and probably let the Toyota dealer handle it so they can deal with the paperwork when it doesn't put the light off or something not so great happens.

You can try a spacer on the downstream O2 sensor and see if that works but you want to get something not a spark plug fowler You want a real spacer it'd be made out of stainless or gold medal or something pretty heavy duty they're about 18 bucks

 

No, the P0420 should only trigger the "check engine" light. The red triangle (master warning light) is usually the result of faults in the hybrid control system. You need a capable scantool to check all systems for fault codes.
(It could be related to your previous repair of the HV battery)
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