Celica Forums General Discussion Engine and Performance Check Engine Light P0420

My Check Engine light came on and I had it diagnosed. The Cat was bad. It's still under warranty for 80K miles or 8 yrs.. My question is if I have the Cat replaced with a new one will I lose any gain or will the new Cat give me any gain. The CEL only come on occasionly after I reset it.

Someone told you it was the catalytic converter? I've been getting that same code, and I was told it was the o2 sensor. Those will go bad before the cat. You might want to check into it.

here's the text for the P0420 code...

P0420
After the engine and the catalyst are warmed up, and while the
vehicle is driven within the set vehicle and engine speed range,
the waveforms of the oxygen sensors (bank 1 sensor 1 and
bank 1 sensor 2) have the same amplitude
(2 trip detection logic)
Trouble area..
• Gas leakage on exhaust system
• Open or short in heated oxygen sensor circuit
• Heated oxygen sensor
• Three-way catalytic converter

INSPECTION PROCEDURE
HINT: Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool. Because freeze frame records
the engine conditions when the malfunction is detected, when troubleshooting it is useful for determining
whether the vehicle was running or stopped, the engine warmed up or not, the air-fuel ratio lean or rich, etc.
at the time of the malfunction.

1) Are there any other codes (besides DTC P0420) being output?
YES Go to relevant DTC chart.
NO

2) Check gas leakade on exhaust system.
NG Repair or replace.
OK

3) Check oxygen sensor (bank 1 sensor 1) (See page DI-49 ).
NG Repair or replace.
OK

4) Check oxygen sensor (bank 1 sensor 2) (See page DI-58 ).
NG Repair or replace.
OK
Replace three-way catalytic converter.


Basically, it could be either your oxygen/O2 sensor OR your catalytic converter.



https://celicahobby.com/forums/ubbt...light-diagnostic-trouble-code-chart.html

My 2000 Toyota Celica GT is pulling up the PO420 code also. I've noticed that the car can sit over night and be completely cold, but when I start it, then turn it right back off, that the exhaust is crackling. What could possibly do that? If I don't have to buy another cat, I won't. I'm only 17 and I definitely don't have that type of money...

I was told the same thing. Cat is bad. But not to worry unless I needed to get a smog done. Was told it doesn't hurt the car in any way shape or form. Just to change it when I have to get the smog recertified. Price on a new cat is at about $500? Is that about right? How much would a new O2 sensor be? The CEL is the only thing that worries me when I drive the car. If a new error is to occur then I wouldn't know cuz I don't have a OBDII myself to reset the code.