Will clear the code/turn off the light and see how long it takes to come back on again.

 

Never had any converter codes with my Turbo but my Boxster would generate a P0430 code every so often. (Was a loose converter brick and it would shift position every once in a while and this would affect exhaust gas flow through the converter.)

(Might add the error code appeared more often when I was using discount premium gasoline. I moved across town and a nearby Shell station was handy and very price competitive and I switched to Shell V-Power and with no other changes the error code appeared less often. At some point the Shell station lost its price competitiveness and I switched to a nearby Chevron station and used Chevron Supreme. The Boxster engine -- by this time with a replacement converter installed -- perked up after a tank or two of Chevron gasoline. My point is you might consider switching to Chevron Supreme or if Chevron not available where you are using a bottle of Techron mixed with a full tank of gasoline to see if this helps. I use the bottle that treats 20 gallons and shake the bottle then dump it into the gas tank and then fill up the gas tank. I seldom use Techron but when I d I repeat the treatment with a 2nd bottle after the tank with the 1st bottle added is almost gone. Then when the 2nd tank is almost gone I have the oil/filter changed.)

Anyhow, back on the error code subject: The SOP at least with stock exhaust is if the code is accompanied by any aging O2 sensor codes replace the indicated sensors (when my Turbo generated an O2 sensor error (P0135 IIRC) I just replaced all 4) then clear the codes and road test the car.

If the P0420 (or P0430) error comes back replace the indicated converter. It is not able to store oxygen.

The converter passages do not plug up except in well exceptional cases where the converter suffers from excessive heat -- which can arise if the car is driven with rich misfires -- which can cause the converter proper to melt and come apart and the particles can block flow downstream.

The converter can get "poisoned" if one runs leaded gasoline. If you track the car and fill up with "racing" gas avoid even low lead gasoline.

Another possible problem is using an oil that is loaded with ZDDP. If the engine consumes some oil -- and it may just from the normal oil vapor that is created in the engine and which is not all removed by the AOS and burned in the engine -- this ZDDP in the heat of the converter forms a glass like coating on the working surfaces of the converter and this naturally reduces the converter's efficiency.

Another explanation is a freer flowing converter may not have the surface area in which to bring all the exhaust into intimate contact with the catalytic metals that coat the working surfaces of the converter.

Or the converter design is such that under some conditions, engine RPMs and throttle openings, the exhaust gas flow is not that smooth and the converter doesn't get an even dispersion of exhaust gas flow. The result is some portions of the converter may receive a disproportionate amount of exhaust gas and in this case the exhaust gas speeds through the converter and the oxygen doesn't get a chance to temporarily bond with the converter metals.

In your car's case you can replace the downstream O2 sensors to see if this helps. When my 2003 Turbo started manifesting a P0135 I had all 4 replaced (they were original and had 132K miles on them) and the engine ran noticeably better afterwards. Kind of surprised me and kind of was expected.

Surprised me because I have replaced sensors on my Boxster before and the new sensors eliminated the error code but the engine was otherwise unaffected.

Kind of expected because as the Turbo engine is a different animal than the Boxster engine and is "harder" on its sensors. Plus the #1 sensors are wide band to help ensure much more precise fueling. As these age then fueling becomes compromised though there was never any CEL indicating a fueling problem. (The sensor error code was due a failed sensor heater.)

I'm not up to speed on O2 extender and such. I know the DME monitors #2 O2 sensor voltages (as it does with #1 O2 sensor voltages) and wants to see the #2 sensor voltages in some way follow the varying voltages of the #1 sensors. The #2 O2 voltages want to signal mainly little oxygen is making it through the converters even though the DME supplies excessive oxygen every so often (about 1Hz at idle and several Hz at higher RPMs) by leaning the mixture. It is the lack of oxygen in the exhaust gases that let the DME know the converter is working ok.

If the DME doesn't get the #2 sensor voltages it wants it will adjust fueling in an attempt to get them and this can lead to less efficient fueling of the engine. If the DME goes too far this could lead to misfires.

 

Replaced failed primary O2 sensors @ 54k, downstream are original. Have 2 new secondary O2 sensors that I will install. Exhaust system is a Max Speed with integrated cats I purchased used...had very few miles on them. Fuel I use in the car( and bike)is Chevron 94 octane...nothing else. Appreciate your input and the time it must have taken you to post it. Will post again when I address my code problem.

 

Decent chance an o2 is failing...

 

Bought 2 new ones last year just in case...now's the time to install them I guess

 

This is how mine started. Then the 420 got accompanied with 302 code. Tried cleaning MAF, changed plugs, coils, reversed oxygen sensors, etc., to no avail. When I changed plugs I was codes free for months (got very excited) only for codes to come back. It's the cats failing! Good fuel helps. I now only use 100 octane (Europe) and it seems I get less codes. It's totally unpredictable but codes always comes back. I clear the codes with iPhone and contemplate the cats change. I found some extenders but no one who would confirm that they actually solve the problem. So, uncertain fix I guess. Bloody pain, I wish someone would just say; this is what you do, it fixes it! OEM cats are prohibitive in cost. Looking at refurbishing options but unsure that will work... Ps. I was told you can disable this code via the tune? Anyone knows about this?

 

Jeeze alot of people writing diaries here . It's the Maxspeed ****ty cats. They're most likely resonators shaped as cats as that exhaust is really cheap. Cheap exhaust = issues sometimes. It's not a bad issue and doesn't harm the car but is annoying nonetheless. The extenders I was talking about are like these

https://www.google.com/search?q=o2+e...hrome&ie=UTF-8


Those will pull the sensor just far enough out of the stream to trick the ECU into thinking it's looking at "cleaner" air and meaning the cats are working fine. You can also just have the rear o2 sensors shut off via coding/tuning.

 

This can also occur if you have a leak from the coolant expansion tank dripping onto the L side exhaust. I got the same code on a relatively new exhaust and was advised of this (along with a bunch of other possibilities) from the exhaust vendor. I was somewhat incredulous, but sure enough I did have a small drip on my garage floor. I replaced the coolant expansion tank cap, the drip is gone, and the code has not returned.

 

Expansion tank is in good condition. Used a vacuum tool charge the coolant system. System held vacuum for about five minutes before charging the system.