2002 fire bird replaced the cat converter all three sensors still getting p420 code

You need to find a mechanic that is smart enough to use a scan tool that is able to view the live data stream and find the source of the issue. The P0420 code can be frustrating as it is usually something insignificant that sets it. Could be a vacuum leak, and exhaust leak, a bad wire to one of the O2 sensors. It takes time with a scan tool to nail down the cause.

Unfortunately, universal catalytic converters do not have enough oxygen storage available and the code will return quickly if you use them. Asian imports are very touchy about this, Subaru's and Toyota's hate aftermarket universal cats!

p420 code has to do with your exhaust system,catylic converters,..sensors...could be a simple fix or not...

replace your rear oxygen sensor ,,,if that does not clear your code after about a 100 miles than you need a cat converter ,,if you have a bundle of miles on it already that will most likely be your issue

Is the code P420 ? Is there an exhaust leak in front of cat? If not you need a new cat. Recommend one from Suzuki. cheap ones don't last more than a year or so. If it was a sensor you would have a different code. Can only be bad cat or exhaust leak before cat allowing fresh air to be pulled in.

P0420 means the cat converters tests below minimum efficiency. That can be caused by an exhaust leak. Take it to a small independently owned (NOT A CHAIN PLACE) shop to get a quote.

Code p0420 is 'catalyst efficiency below threshold'.

This could be caused by a bad catalytic converter but before dumping a ton of money on that I would suspect the after-cat oxygen sensor is getting lazy and setting the code.

Have the O2 sensors checked and replace if needed before suspecting the catalytic converter.

Good luck.

Hi

The trouble areas associated with this code are as follows:
1)Gas leakage on exhaust system
2)Oxygen sensor
3)Heated oxygen sensor
4)Three–way catalytic converter

The idea is to check for exhaust leaks first then the front sensor and rear sensor. If these all check out then the cat needs to be replaced.

Hope this helps. Thanks for using fixYa

Code p420 is a code for catalytic converter enefficiency. This can be caused by a few problems. The vehicle uses two sensors one before and one after the cat. The sensors determine how well the cat is doing its job based on how much oxygen is sensed in the air based on the rule of thumb of 21% in our atmosphere. You mentioned that these were replaced once before, and i hate to knock another technicians work without seeing it but it could be possible that the cats he installed were not OEM parts and just a generic. You can get this code from using a non vehicle specific part like that, aseasily as you can get it from a faulty pre or post cat o2 sensor.
best thing i can suggest is getting the car on the scanner and having a buddy drive it on the highway at a steady rpm, watch the 02 sensors and see if there is erattic movement or sticking, from there we can findthe next step, and FYI all catalytic converters come with a Federally Mandated Warranty period of 8 years 80,000 miles, so dont ever pay for new ones again.

the cat is bilt into manafold and the sencer is just up abuve it