P0420 is catalyst below threshold. It is triggered via the rear o2 sensor (post cat), so you may want to check that sensor to make sure it's functioning properly.
Usually caused by worn out catalytic converter, but may also be the downstream O2 sensor: Catalytic converter system, bank 1 - efficiency below threshold
Catalytic converter, wiring, HO2S 2
SOURCE: amplifier location 1993 lexus es300
My Son has a 95 es300, the amp for it is located under the front passenger seat. The easiest way to access it is to remove the 4 bolts holding the seat down, and remove the seat. Takes about 5 minutes
SOURCE: 2002 Lexus ES300 Check Engine Light
You can disconnect your battery for a short period of time, 5-10 minutes should do it. There is no guarantee that the check engine light will not come back on in time, but it will make it go away at least temporarily.If you go to Autozone, 99% of the time they will hook up a code reader and diagnose your problem. It may be a minor and/or inexpensive fix. Please vote appropriately and leave feedback. I hope this helps and good luck.
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SOURCE: LEXUS es300 oil light stays on oil level full
Check oil level sensor, replace if necessary. also, does your engine knock or make a tapping sound?
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