Po420 code

Hello All, I have a PO420 code. Would the place to start be replacing the O2 sensor? Thanks in advance!

Quotes source post: 11838354

P0420 - Catalyst System Efficiency Below Threshold (Bank 1). Essentially this means the converter is not able to store oxygen. The SOP is if there are any active (or pending) O2 sensor aging codes with the P0420 (or P0430) to replace the sensors indicated and clear the codes and road test the car and if the P0420 error comes back replace the converter. Do you hear a buzzing noise like a loose heat shield from the car? If so this can be from a loose 'brick" in the converter and the converter is performing below par because being loose it is not getting the full benefit of the exhaust flow. The converter needs to be properly positioned in the exhaust gas stream so all exhaust gases flow through the converter. This helps to keep the conveyer hot directly from the exhaust gas heat but also from the chemical reactions that take place with the exhaust gases as they pass through the converter. If the noise is present and coming from the converter you are faced with replacing the converter. Has the car been recently worked on? While I doubt this can be the cause an exhaust leak if present can create problems with the converter. What you can try is switching to a name brand top tier gasoline. When my Boxster had an underperforming converter -- due to a loose brick -- I found the error more likely to appear when using a discount gasoline. Even with a name brand (Shell) gasoline in the tank the error did still appear but its frequency of appearance was a lot less. You can try a bottle of Techron -- use per directions on the bottle. At the same time take a nice longish 40+ mile drive at highway speeds. This will work to remove deposits from the intake and exhaust valves, combustion chamber, piston and possibly even the O2 sensors and converters. The engine will run better and this means less work for the converters. Be sure the engine is in good tune. This means if the plugs are due to be changed they should be. Be sure the air filter is reasonably clean and free of buildup. The oil wants to be reasonably fresh and the engine not overfilled with oil. Oil with too many miles on it is contaminated oil and contaminate oil creates more oil vapor -- as does an engine overfilled with oil -- and more oil vapor means the engine has more oil vapor to burn which means more work for the converters. Understand there is no magic bullet. All of the above will help some -- over the years it helped my car pass smog checks -- but at some point the converter will have to be replaced. Factory converters are expensive. Depending upon where you live aftermarket converters may not be a legal option and even if they are they can come with drawbacks: Louder, with droning, ill fitting and not as efficient. Good converters require (among other things) a goodly amount of catalytic metals to efficiently process exhaust gases. Even though converters have just very small amounts of these metals present, the metals have to be properly spread out to maximize the active surface area, as these metals are very expensive and one can't just slather them on. When the rattling from the loose converter became louder, and the car failed a smog check -- though after a nice drive and a return to the test station it passed with flying colors -- what I did was I broke down and bought a set of used (salvage) converters and had these installed. Trouble is I learned just recently -- after I had done this -- this is illegal so I can't recommend you do this. So what one is faced with now is factory converters or possibly aftermarket if any are approved for use where you live/drive.

Thanks for the detailed response! There is no rattling sound. Engine was completely rebuilt about 10k miles ago and runs perfectly. There is a possibility I may have slightly overfilled with oil. Oil in the car is not too old.......about 4000 miles and 5 months, Joe Gibbs DT 40. I put standard Canadian 91 octane in the car. If we get some warmer weather, I could put some Sunoco 94 in and take it for a blast. I will try that and the Techron and then reset the CEL and see what happens. Thanks again.

Which gas station has the best gas?

Quotes source post: 12725324

I've run Shell, Chevron, Philips 66, UNOCAL and for a time various discount gasolines. When I was running discount gasoline a bad converter error would occur more frequently. A switch to Shell -- prompted by a move to another part of town and the Shell station being quite convenient to my new location -- I noticed the converter error occurring less frequently. So I stayed with Shell for several years. What I found recently is a switch from Shell -- my local Shell station upped its prices to 10 or 20 cents higher per gallon for no apparent reason -- to Chevron after a tank or two really perked up my 2.7l Boxster's engine. Even though my usage remained the same I attributed this change for the better to the detergents in the gasoline, primarily Techron. Might add that I switched from Shell to Chevron with my Turbo too and I can't report any change for the better -- or worse. My WAG is the Turbo is a cleaner running engine -- maybe in part because it has just 138K miles vs. 295K miles for the Boxster engine (though the Boxster engine doesn't manifest any indication of its miles in any way I can tell) -- and as a result the engine doesn't benefit as much from Techron. Last but not least, buy from a busy station to ensure you buy the freshest gasoline. Porsche guidelines offer that if the engine reacts unfavorably to a particular gasoline to try another brand. In all the brands I have tried I have never noticed the engine in either car reacting unfavorably. So around my usual haunts I fill up with Chevron as it is the least expensive gasoline -- at least compared to the nearby Shell station -- and on the highway any number of name brand stations, whichever one is convenient when the car needs gasoline.