Check engine light on 2001 toyota prius

Check engine light came on, was diagnosed (at retail auto parts store), as systems weak (spark plug replacement suggested), second diagnosis at independent resulted in O2 sensor: replaced with after-market sensor. Drove 20 miles check engine light came back on. Next time I tried to drive it , it would start but would’t move. Main battery indicator showed severe drain. Towed to dealership. Dealership replaced O2 sensor with Toyota part and replaced a relay (perhaps an ignition relay). Drove a few hundred miles and the check engine light came back on. Independent re-diagnosed as catalytic converter. He reset the computer so that the light went off. Drove 70 miles (meanwhile car passed emissions inspection), drove a few hundred more miles and the check engine light came back on again. So what do I do now? Sell it? Keep on having it diagnosed and repaired? Is it worth it? How much life left in the batteries?

How Many Miles Are On This Vehicle ? Other Than This, Is The Car’s Condition Very Good ?

These o2 sensor replacements with repeated “check engine” lights are turning into a very popular topic,I struggle to come up with a check list to handle the situation.

Your situation is complicated by the expensive battery situation.

Have it looked at again. It may not be the O2 sensor or cat this time.

Let’s get the real codes not someone’s interpretation. The code should be in the format (P0123) There may be more than one code.

89000 miles. Yes, the condition is very good.

a re-test came up with these codes:a)from independent non-certified [P0420]catalytic
and b)from ‘Autosome’[P0420] O2 sensor bank 1, and[P3191]fuel air meter auxilliary emission control massive air flow sensor.

Had it looked at again, and the results appear in the next post below.