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Bound to happen. I finally got my first P0420 code!

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Old 05-01-2014, 11:37 PM   #22
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Originally Posted by RecklessTaco View Post
Dont long tube headers and a y-pipe eliminate cats all together? so how is that legal if all states require cats
long tubes eliminate the cats, not the y pipe. the y pipe has resonators.
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Old 05-02-2014, 07:33 PM   #23
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Bill do you mind continuing about covering the process for diagnosing the components? I just had my muffler and pipe replaced up to the cat, but still throwing a p0420, so will have to get the multimeter and test sensors and maybe the cat. Also gonna disconnect the battery to reset and change spark plugs since it had been running way rich for quite some time, and clean the TB, IACV, and MAF while in there.
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Old 05-02-2014, 07:40 PM   #24
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Quote:
Originally Posted by fyremanpat View Post
this sounds crazy but try cleaning your MAF. if the ECU is getting a false reading due to a dirty MAF it can throw a P0420 code. I went through this on my old truck after dropping over a $1000 on new cats and o2 sensors only to find out a $7 can of MAF/MAS cleaner did the trick. Hope this helps!
What year was your truck that you dumped money into? Mines an 05 and really don't want to changeout the whole manifold, cats, etc.
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Old 05-02-2014, 07:46 PM   #25
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I couldnt imagine an 05 to warrant a repair that extensive, even with my rotten frame and underbody they didnt try to sell me on sensors & cats up to the manifold. Not sure what year his truck was, mines an 03 so i guess 2 years isnt much time difference especially if you live in a rust prone area.
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Old 05-03-2014, 12:22 PM   #26
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Quote:
Originally Posted by Mrogers33 View Post
Bill do you mind continuing about covering the process for diagnosing the components? I just had my muffler and pipe replaced up to the cat, but still throwing a p0420, so will have to get the multimeter and test sensors and maybe the cat. Also gonna disconnect the battery to reset and change spark plugs since it had been running way rich for quite some time, and clean the TB, IACV, and MAF while in there.
I will update as I run the diagnostic. The shop has been really busy as of late and I just never seem to have time to work on my own sh!t! haha
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Old 05-03-2014, 12:27 PM   #27
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Quote:
Originally Posted by BamaToy1997 View Post
I will update as I run the diagnostic. The shop has been really busy as of late and I just never seem to have time to work on my own sh!t! haha
I would love to see it to cause I never diagnosed my 99s P0420 that I PM'd you about awhile back. Subbed for the long run
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Old 05-06-2014, 07:18 AM   #28
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I haven't forgotten about this, just to let you all know. I am trying to get the time where I can diagnose it, and document everything.
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Old 05-22-2014, 07:36 AM   #29
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NOTE: I would have more information posted, but I have not had the code fail again since the starting of this post. All O2 data is normal, and everything checks out. Just thought I should update.
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Old 07-14-2014, 02:18 PM   #30
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Quote:
Originally Posted by BamaToy1997 View Post
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Common questions I receive:
What does P0420 mean?
Do I need to replace my cat?
How does the computer know my cat is bad or not?

P0420 has been one of the most undesired codes for any vehicle owner, be it Toyota, or any other manufacturer. They can be tricky for some people to diagnose and can be expensive to repair. Since 2006 all vehicles sold in the US are required to be OBDII compliant. This means that no matter WHAT communication type is uses (CanBUS, ISO, etc) certain trouble codes must have the same number, and same meaning. So a P0420 in a Toyota means the same thing as a P0420 in a Chevy, Ford, Hyundai, etc. It also means that the threshold minimum standards are all the same for each code. This means that if you can diagnose a P0420 in a Toyota, you can do it on any other vehicle.

What does P0420 mean? P0420 is defined as: Catalyst System Efficiency Below Threshold (Bank 1) EVERY vehicle will have this code available. Certain "V" configuration engines (V6, V8) will also have P0430 if there are dual cats NOT in sequence. The Tacoma with the 4.0 V6 has a cat for each "bank" or side of the engine. Diagnosing P0430 will essentially be the same.

The first step in diagnosing the code is understanding HOW the code sets, and how the ECU runs the test. The major components of the P0420 code are:
  1. Three-way catalytic converter
  2. The ECU
  3. A/F sensor
  4. Post-cat O2 sensor
Three way catalytic converter

It would take a good bit to explain the intimate details of how a catalytic converter works, so I will simplify it enough to this: It take the exhaust coming from the engine and chemically alters it to reduce harmful chemicals from entering the atmosphere. The worse condition the exhaust is, then the harder the catalytic converter has to work to "clean" the exhaust.



What does this mean? You should always make sure that your engine is running as efficiently as possible. This means proper maintenance. Change your spark plugs as recommended, and keep your air filter cleaned, or replaced. A dirty air filter can actually cause catalytic converter problems. An engine running at a perfect (stoichiometric) air/fuel ratio of 14.7:1 will produce the least amount of harmful gasses in the first place, so the first step in checking for a problem is to make sure your engine is running efficiently.






ECU

So how does the ECU figure out if the catalytic converter is doing it's job? First off, the ECU will never test a cat that is not warmed up. A cat cannot do it's job if it is not at temp. So trying to "test" for a P0420 without warming up the car will give you inaccurate results. After the vehicle is warmed up the ECU will also wait to run this code diagnostic until you are cruising above a speed between 40 and 70MPH. It will NOT however typically run the test if you are at a steady cruise speed. The ECU will also only perform the test ONCE for the drive cycle, so once it runs and either passes or fails, it won't test it again until the ignition is cycled. It take approximately 30 seconds to perform the test itself, but it may take a full 10 minutes of driving to run it.


A/F Sensor
The A/F sensor, while looking identical to an Oxygen sensor, works under a narrower and more "detailed" inspection of the airstream in the exhaust. It not only measures the oxygen content, but is also capable of minute detections of variations. Perhaps the simplistic version that would be easier to understand is imagine your TV is the ECU, An O2 sensor give the TV a 720P picture, and the A/F sensor gives your TV a 4K signal. This means that the ECU can make much faster, and more detailed adjustments to the fuel ratio, making the engine run more efficiently.


O2 Sensor
The O2 sensor after the catalytic converter measures the airstream AFTER the catalytic converter has "cleaned up" the exhaust. It does not need to be as detailed as the A/F sensor, because it's sole purpose is to monitor the catalytic converter. It has no effect on fuel trim, or anything else. It simply monitors the Catalytic converter.



Self diagnostic process

So while you are driving along the ECU will enrich, or lean out the fuel mixture. This alters the exhaust content that enters the exhaust system. The ECU will expect to see this change in the A/F sensor before the cat, and it will expect to see very little change in the O2 sensor after the cat. Anything out of what is expected (Based on the pre-programmed data for the code test) will flag a potential code. (This is when your Ultragauge beeps with a "pending code) This failure must occur twice, in two consecutive drive cycles, before it will set a hard code, and turn on the CEL.


All of this leads us down to the main question: How do I diagnose the code and replace the RIGHT defective part, and not just be replacing parts on a guess?


A poor condition A/F sensor can cause some chance of a P0420 code, realistically it is the least likely culprit. In my 25 years of being a tech, I have only ONCE replaced a sensor before the cat for a P0420/0430 code.



A poor condition O2 sensor after the cat would most always guarantee a P0420/0430 code. The ECU expects to see a near flatline signal if the cat is working properly.



A bad catalytic converter will typically result in a high waveform of the O2 sensor all the time. Below is a picture of the various waveforms and what you might see.




On the left is a normally operating cat. On the right, a cat that has deteriorated performance. Note that the A/F sensor reads pretty much the same either way. That is because it is upstream of the cat.


So how can YOU test the sensors and the cat so that you know what part has failed? You CAN test with a simple, quality volt meter, but it is not really easy. Using your Ultragauge or Scangauge, while giving you data, has a much too slow of a response for a valid diagnosis. This unfortunately results in the need for a diagnostic scan tool. Not everyone has access to this, thus the need for a good volt meter!

NEXT: I cover the process for performing the diagnostic process.
I am attaching my waveforms. The graph appears to indicate that I have a bad cat because the 2nd waveform on mine somewhat follows the first, which is indicating that the expected O2 level does not meet Federal emissions specifications, correct? Is that why it is not a flat line as expected for normal emissions? If a sensor was consistently bad, I would not have these waveforms and good voltage output, correct? The pick on the left is 50MPH, the one in the middle was immediately after engine reached operating temperature and I reached a steady 45MPH. The pic on the right is at 70MPH.
Attached Thumbnails
Bound to happen. I finally got my first P0420 code!-o2_55mph.jpg   Bound to happen. I finally got my first P0420 code!-o2-starting_at_engine_op_temp.jpg   Bound to happen. I finally got my first P0420 code!-02-70mph.jpg  
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Old 07-17-2014, 01:34 PM   #31
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I clicked a wrong button and had about 3 nice paragraphs deleted on accident! Grrr. Well, cut to the nitty gritty, Those waveforms actually look pretty decent. You don't want to go by a reading anywhere except a steady throttle, with no recent acceleration or deceleration (Enrichment mode, and DFCO mode)
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Old 07-17-2014, 06:00 PM   #32
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Quote:
Originally Posted by BamaToy1997 View Post
I clicked a wrong button and had about 3 nice paragraphs deleted on accident! Grrr. Well, cut to the nitty gritty, Those waveforms actually look pretty decent. You don't want to go by a reading anywhere except a steady throttle, with no recent acceleration or deceleration (Enrichment mode, and DFCO mode)
Thank you. The CEL came on again and getting the infamous 'catalyst system error' again. How can I run like this before the O2 sensors or something related begins to fail too? I am shopping for a new cat because the voltage looks good on the O2's as you were saying. P0420 go away!
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Old 07-19-2014, 12:32 PM   #34
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Ford technician here. My taco got the bank 2 drivers side code a few months ago and I mostly ignore it. I used our snap-on scanner and determined that it is indeed the cat and because it's part of the manifold from Toyota it's a grand for the part.

Any one have aftermarket recommendations?
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Old 07-19-2014, 12:40 PM   #35
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Quote:
Originally Posted by netsomnia View Post
Thank you. The CEL came on again and getting the infamous 'catalyst system error' again. How can I run like this before the O2 sensors or something related begins to fail too? I am shopping for a new cat because the voltage looks good on the O2's as you were saying. P0420 go away!
You want to be at idle sensor one should be an up and down wave sensor two should be almost flat. If one and two match or close to it you have a bad cat like I do
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Old 07-23-2014, 04:26 PM   #36
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Originally Posted by evile View Post
You want to be at idle sensor one should be an up and down wave sensor two should be almost flat. If one and two match or close to it you have a bad cat like I do
Thank you. CAT it is. I am thinking Maganflow aftermarket and keep replacing it as it needs it. Hopefuly it will last more than a couple few thousand miles. When I first bought the vehicle the gasket before the cat was leaking so I think this might have been how the CAT was damaged or contaminated in the first place.
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Old 07-23-2014, 04:33 PM   #37
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Quote:
Originally Posted by BamaToy1997 View Post
What was the specific code? Was it P0420, or something else close?
P0240. You said those wave forms looked good but after reviewing this doc: http://www.obd-codes.com/p0420 , second paragraph under "What does that mean?", I am leaning towards a CAT. Do you have something else in mind for troubleshooting or do you think I am diagnosing properly?

Quote from obd-codes.com: "The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar."

NOTE: They appear to be normal like your example while idling but both fluctuate and nearly match when driving down the road and closely matching at high speed (60 MPH+). I'll pull the trigger on aftermarket CAT tomorrow unless you think I need to disconnect O2's and do more testing with volt/ohm meter.
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Old 07-24-2014, 06:04 PM   #38
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Sub'd. I have this code on both my wife's Jetta and the Taco now... Really helpful stuff here, I love this forum.....
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Old 07-25-2014, 09:37 AM   #39
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This code just popped up on my 01 Taco up yesterday...grr
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Old 07-25-2014, 04:58 PM   #40
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Originally Posted by Funhog View Post
This code just popped up on my 01 Taco up yesterday...grr
Bound to happen. I finally got my first P0420 code!-tacoma_o2_ohms.jpg
I think I overlooked this diagram and a related thread during my research before I ordered cat. My new CAT is on the way but this attachment might help you pinpoint better. I thought if my O2's were responding in ODBII graphs that would be enough diagnosis, but other 1st Gen. threads indicate that the downstream O2 is a more common solution for the P0420 code. Who knows? Looks like I will be testing Ohm's with my volt/ohm meter while my CAT is being shipped.

Here is the other O2 reference thread that I am referencing for a PCV troubleshoot: http://www.tacomaworld.com/forum/1st...pvc-valve.html
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