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Recently purchased used 2005 Tundra V8 4.7L. It has 100K miles and is getting P0420 and P0430 codes. The truck has been in NH its whole life. I've read the threads on these codes and learned a great deal. Here is what I know:

1. Previous owner said he recently replaced two back O2 sensors.
2. I replaced two front O2 sensors with Bosch (actually Denso) O2 sensors last week.
3. Ran two rounds of Techron through it.
4. Replaced PCV valve
5. Previous owner said Toyota Dealership said replace the cats (seems like this is standard $1500 advice).
6. When I clear the codes - they stay off for at most two days, usually back on within a day.
7. Previous owner explained the truck was running rough at about 85K miles. It ran that way for awhile and then he replaced the plugs and things got immensely better. Apparently there was one very bad plug.

So.. I am at crossroads, I can get two Magnaflow Direct Fit Catalytic Converters for a total of $500 - not a bad deal. But wanted to hear anyone out there comment on my situation and specifically comment on whether #7 above would contribute to premature damage to Catalytic converters. THANKS!
 

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I havent heard anything good about the magnaflow cats. theyre high flow but perhaps too high flow and they dont clean the exhaust as much as they should, tripping the sensors for a P0420 code again.

In my tacoma, it was throwing this code and I had the cats replaced under the 8 year/80,000mile emissions warranty which would have been a $1,500 job. so far (2 weeks) it hasnt thrown the code again
 

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Discussion Starter #6
I did find that as a pattern on this site (after the purchase!)... and am considering purchasing the Denso's and trying to return the Bosch... how about spark plugs - any recommendation on type? style?
 

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I did find that as a pattern on this site (after the purchase!)... and am considering purchasing the Denso's and trying to return the Bosch... how about spark plugs - any recommendation on type? style?

Our Tundras do not play well with Bosch at all. I had endless CEL as a direct result of Bosch O2 sensors. Stick to Denso for the O2 sensors and use Denso or NGK spark plugs.
 

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I pulled out some cheap Bosch plugs (Super Plus) and replaced with NGK Iridium... let's see how that goes.. next stop is the O2 sensors.. switching from Bosch to Denso..
 

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New plugs did not do it as light came back on soon thereafter.. I replaced new Bosch pre-cat O2 Sensors with Densos... I will report back.
 

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Make sure all the O2 sensors are Denso. Here is something you should read about replacing cats with aftermarket non-Toyota cats:

Notes

  • Most Toyota vehicles need an OEM Catalyst, especially if there is a Catalyst-related software update required. Toyotas usually re-set the P0420 code unless an OEM catalyst is used as a replacement. It is common for mechanics to replace all the Oxygen sensors only to find that the Toyota vehicle required an OEM Catalyst.
  • Toyota has extended their catalytic converter coverage beyond the typical Emissions Warranty which is 3years/50,000 miles, which ever occurs first. On many Toyota vehicles the Catalytic Converter warranty has been extended to 8years/80,0000 miles when ever a code P0420 occurs. And on very specific years and models the Catalytic Converter Warranty has been extended even further.
  • If you call to inquire about the warranty, have your VIN code ready to be checked in the Toyota database, if you just call to ask about what is covered, typically the dealership will only tell you the minimal coverage. You need to be proactive and ask a Service Writer, not a phone receptionist, to check your VIN code for the most up to date warranty information.
  • Many Toyota Catalytic Converter warranties have been extended to cover the repair of a P0420 code. This is being done on a year and model basis so be sure to have your mechanic call a Toyota Dealership and check your VIN code to see if your Catalytic Converter warranty has been extended.
  • Presently, most of the aftermarket Converter companies have re-worked their designs so they can be certified for use in OBD-II vehicles in California.
  • After the new Catalytic Converter has been installed, most modern Toyota vehicles (2002–present) will need a software update programmed into their PCM.
The Basics
The Catalytic Converter looks like a muffler. It is typically a stainless steel housing over a ceramic honeycomb core. The catalyst itself is made of platinum, palladium, or rhodium, all rare metals, which is why Catalytic Converters are so expensive. These elements reduce the toxicity of harmful exhaust gases that are expelled from the tail pipe. Catalytic converters are quite efficient, but if engine maintenance is neglected or an engine is allowed to "run rough," damage could occur, resulting in costly repairs. To replace the Catalytic Converter, the vehicle is raised to gain access to its underside. The converter is removed from the exhaust system and the new Catalytic Converter is installed.

Want to Learn More?
The Catalytic Converter is a sophisticated after-burning device designed to complete combustion of the exhaust gases that pass through it. It is a stainless steel container with an inlet and outlet pipe that looks similar to a muffler. Inside, the Catalytic Converter is a ceramic monolithic structure that has honeycomb-like passages running though it. This structure has several sections called beds that are thinly coated with rare metals, which react with the compounds in the exhaust gases to complete the combustion process, thereby cleaning the exhaust of harmful emissions.

  • The first section of the Catalytic Converter is called the reduction bed and is coated with rhodium. It is called the reduction bed because its purpose is to reduce the NOx gases back into harmless nitrogen and oxygen.
  • The next section of the Catalytic Converter is the oxygen storage bed, which is coated with cerium. Its purpose is to maintain an ideal level of oxygen for use by the rear of the converter. It does this by storing and releasing the oxygen that gets released from the reduction of NOx in the previous reduction bed.
  • The oxygen is then available for use in the final oxidizing bed, which is coated with platinum and palladium. The purpose of the oxidizing bed is to complete the combustion of CO by adding oxygen. The oxidizing bed also uses oxygen to burn any of the raw HCs that still remain in the exhaust gases.
P0420 Diagnostic Theory for Shops and Technicians
The P0420 code is set when the Catalyst monitor sees a decrease in voltage from the rear Monitoring Oxygen Sensor(s) and an increase in switching activity—from rich to lean to rich, etc.—that closely resembles the front Oxygen Sensor(s) during the time the computer is activating the Catalytic Converter monitor test. The voltage threshold is usually a minimum of 650 millivolts, which indicates a low level of oxygen. When the voltage goes too far below the 650 millivolt minimum, it indicates a higher level of oxygen. This means that not all of the oxygen is being consumed by the combustion process or by the afterburning effect of the Catalytic Converter. When the oxygen level gets too high, it means that the Cerium or Oxygen storage bed has degraded to the point where it is no longer able to store oxygen created by the reduction of NOx (nitrogen and oxygen). This oxygen is essential for the rear Oxidation bed to complete the conversion of CO into CO2 and HCs into H20 and CO2.
Common Tests for Diagnosis of the P0420 Code


  • Retrieve the code and write down the freeze frame information to be used as a baseline to test and verify any repair.
  • If there are any misfires, ignition, fuel and/or intake problems, these must be repaired before the Catalyst code is addressed. Any misfire, ignition, and/or fuel system problem will quickly ruin a Catalyst. They are often the cause for code in the first place.
  • Test drive the vehicle at or near the freeze frame conditions to verify that the rear Catalyst Monitoring Oxygen sensor is either mirroring the front Oxygen sensor and/or is not reaching the 650 millivolt threshold during 55–60 MPH cruise conditions. If either of theses conditions can be easily verified, then the Catalytic Converter is defective.
  • If there is any doubt about the condition of the front and/or rear Oxygen sensors, then check the Mode 6 data for all the Oxygen sensor monitor tests. If any of the front or rear Oxygen sensors barely pass their Mode 6 tests, then clear all codes and perform a drive cycle to see how well the front and rear Oxygen sensors pass their Mode 6 tests. They need to pass the Mode 6 tests with flying colors or they will confuse the OBD-II diagnostic software and possibly trigger a false code P0420. This is an important concept because if the front Oxygen sensor is slow and barely passes its monitor tests, it can fool the computer into thinking that the Catalyst has failed because the computer just watches how closely the switching speed of the front Oxygen sensor compares to the switching speed of the rear Monitoring Oxygen sensor. If the rear Monitoring Oxygen sensor is losing bandwidth and not able to easily reach the 650 millivolt threshold—but still barely passes its monitor tests—then it, too, can fool the computer into setting a P0420 code.
http://repairpal.com/OBD-II-Code-P0420-Toyota
 
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Discussion Starter #12
thanks for relaying this info... lots to digest.. quick questions:
1. I will assume that an after-market CC, specifically the magnaflow direct fit (i.e. Magnaflow model 93398) is not OEM grade. Correct? I need to use Toyota OEM only?
2. The article says, "Any misfire, ignition, and/or fuel system problem will quickly ruin a Catalyst. They are often the cause for code in the first place." Does ruin mean permanently ruin? For example, I was told by the previous owner that there was an ignition problem fixed by new plugs. The problem apparently went on for a bit of time - would that issue have potentially ruined the cat to the point it needs to be replaced?

From here - I already wrote a letter to Toyota New England and National stating that this problem was discovered at 4 years and 84K (dealer documented in mytoyota.com in 2009 - Hurlbert Toyota quoted $3500 for two new cats - not including O2 sensors!) and asked they they would honorably assume some costs. I'm also going to confirm the post-cat 02 sensors are Densos and if not, replace them. If they aren't Densos then they are going to need to be replaced anyhow. Thanks
 

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End result.. replaced new Bosch O2 sensor up front as well as back O2 sensors with Denso - now the CEL seems to have cleared. Moral of the story - use Denso.
 

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End result.. replaced new Bosch O2 sensor up front as well as back O2 sensors with Denso - now the CEL seems to have cleared. Moral of the story - use Denso.

Glad to hear it - much cheaper than a catalytic convertor.
 

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Had a P0420 Code for the last year or so on occasion, but has been more steady the last three months, replaced my cat with an aftermerket one ($100) two weeks ago and haven't seen the CEL since.
 

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Sounds like, for that price, you installed a universal fit cat. Good to hear you haven't had the check engine light on. Other posting give a mixed report. I got a price of about $500 for two direct fit Magnaflows, but looks like I won't need to purchase them (happy). Thanks for your info.
 

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Had a P0420 Code for the last year or so on occasion, but has been more steady the last three months, replaced my cat with an aftermerket one ($100) two weeks ago and haven't seen the CEL since.
What is the make on those cats? I had the driver's side go out to the tune of nearly $1500 to be replaced by the dealer. No problems since replacing with OEM but OOUCH!!
 

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Discussion Starter #19
The brand for $500 (for direct fit) was Magnaflow... dealer is over $3000 to install both.. I could not believe it.
 

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How can i find if my vehicle is one that Toyota has extended the warranty on a catalytic converter. Service Writer may have no idea what i'am trying to find out about.. Thanks
 
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