2003 pt cruiser ,i had bought a new catalyic converter just looking for someone who can weild it . Previously i had check engine light and oreylies said to change oil pressure sensor and oxygen sensor. I changed oil sensor then light went off for a week then came back on. Auto zone said catalyic converter was below threshold but after traveling 350 miles the light went off . Was wondering why is it off when there is a problem with car when nothing was changed for the catalyic converter.
My check engine light comes on and goes off just about every 50 to 100 miles driven. I had my catalytic converter replaced and then got P1133 on my OBD2. Changed both O2 sensors twice and still get that Check Engine light. My only problem is that I have to time it just right to take my truck to DEQ when the light is out because I have to drive 25 miles to DEQ. This has been going on for over 5 years now with my 97 S-10 p/u.
A P0420 code means the catalytic converter is not working good enough to meet the minimum requirements or threshold needed. The converter needs replacing. You can't expect a cheap after market converter to work well enough to keep the code from resetting. Only WALKER or DORMAN make after market converters that have a 75% chance to work properly. Converters usually bolt on. It's the exhaust system flex pipes that get welded on. Quit listening to salesmen at auto stores.Oil pressure sensors have nothing to do with the converter, The 02 sensors are good ore the P0420 code would not have set.
P0420 is produced by the ECU when the downstream O2 sensor (bank 1 for P0420, P0430 for bank 2) reports a high and fluctuating level of oxygen in the output of the converter. Although it is true the converter is not working right, it is almost always due to bad mixture coming in. If the code definition were changed from catalyst efficiency below threshold (which is true, but not the cause) to excess oxygen in exhaust (which is more accurate and useful) not many mechanics would replace the catalytic converter. The devil of it is replacing the catalytic converter usually clears P0420. for a while. (As thebax2006 says, it is a crap shoot even with the best converters.) After about 2 years the new wears off the converter and the underlying condition gets worse, so the code returns. A new, top quality, converter will usually buy another few months and the code comes back, leaving the owner many thousands of dollars poorer and back where they started. Demsey Dumpster (another answer) fell into that trap even though his is 100% certain to be in mixture control. There are two general causes of P0420: poor mixture control and an exhaust leak ahead of the catalytic converter. A muffler shop can test for and repair exhaust leaks for an affordable price. After that, the next focus is the fuel/air system, including the MAF sensor.
