2006 Chrysler Pacifica. Code P0420. Replaced the catalytic converter a year ago. The check engine light came on a couple months ago and displayed this code again. The light then went off. Now it's back on. How can my catalytic converter be bad in a year?

P0420 Catalyst System Efficiency Below Threshold Bank 1

https://www.autocodes.com/p0404_chrysler.html

catalytic converter is bad - replace it

you will get this code when the incompletely burned fuel in the cat has built up to a certain level and cat can no longer absorb more. The cause of incompletely burned fuel in the cat can be due to many reasons:

1. sparkplugs not firing correctly (wrong gap or fouled)(problem with ingntion components(wiring to spark plugs to high resistance)
2. fuel injectors are fouled.
3. bad fuel, incorrect fuel (regular vs premium-see user manual)

You will have to verify plugs are good, plug wires are good, injectors are clean, fuel is good.

once you get these things line out the light will eventually go out.

thje po420 need to monitor o2 sensors to verify if you have a bad sensor or bad catalitic converter
the po522 oil presure sending unit

scan for stored faults then diagnose rather than throwing parts at it

P0420 is a catalytic converter inefficiency code. Basically the cars computer is looking at the rear O2 sensor to monitor the catalytic converters ability to properly reduce emissions. If the computer sees the rear O2 sensor acting differently than normal it interprets this as the cat no longer able to do its job and turns on the check engine light to make you aware there is an issue. There are a few things that can cause this to happen. The most common is that the catalytic converter has gone bad and needs to be replaced. The good news is the federal emissions warranty on these is typically 8 years or 80,000 miles. Sometimes longer if the manufacturer chooses. If you fall into this guideline call you local dealer and see if you are covered. If you are you will be able to have this replaced at no charge. The bad news is if you are not covered than you will have to pay for it out of your pocket and they are not necessarily cheap. Do not go with anything but either the o.e. cat or a direct fit from a put able supplier. Anything other than these two options will leave you with more problems than they solve. Let me know if you have any questions and I'll do my best to answer them. Thank you for using FixYa.com!

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

http://www.obd-codes.com/p0420

TSB Number: 3316 NHTSA Number: 10017210 TSB Date: n/a Date Added to File: October 27, 2005 Failing Component:Electrical System Summary:Diagnostic trouble code P0420 may set on low mileage vehicles, or shortly after catalytic converter replacement
TSB Number: 3316 NHTSA Number: 10017210 TSB Date: n/a Date Added to File: October 27, 2005 Failing Component:Electrical System Summary:Diagnostic trouble code P0420 may set on low mileage vehicles, or shortly after catalytic converter replacement
there is a service bulletin for this.

http://www-odi.nhtsa.dot.gov/cars/problems/tsb/results.cfm?start=1&SearchType=DrillDown&type=VEHICLE&year=2005&make=CHEVROLET&model=COBALT&vehtype=PC&typenum=1&component_id=0&summary=true

Hello: Code P0 420 indicates the catalytic converter is operating below calibrated efficiency (below 60%) replacing the oxygen sensors will not correct the condition. The converter needs to be replaced and the code cleared.

The catylitic convertor is almost plugged up fully or the 02 sensor may have been degenerated
have these items checked out before more related emission items go bad down the line

You need a new Catalytic Converter

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

There is one 02 sensor in front of the catalytic converter (called upstream), and one behind it (downstream). When the engine is warmed up and running normally the upstream oxygen sensor reading fluctuates and the downstream one is fairly steady. In the case where both readings are fairly steady, a P0420 check engine light code is set.

Possible Causes:
Oxygen (O2) sensor not working correctly
Damaged or leaking exhuast (pipe, manifold, catalytic converter)
Damaged catalytic converter