P0420 AGAIN

Hey dudes, its been a year or so since i was here and now im back... with the same issue. Really hoping ya'll can help point me in the right direction again (you guys saved my ass so many times financially and taught me a lot about trucks).

Background: I bought a used 2002 pre-runner just a little over a year ago. previous owner reset the CEL lights when demo'ing the truck to me. After purchasing the truck and about 100 miles later I got a CEL P0420 code. After doing a lot of research and such I replaced the Front and Rear o2 sensors as well as the first main catalytic converter (with a magnaflo recommended by my mechanic). The order in which I did this was, Front o2 sensor, Catalytic converter, THEN Rear o2 sensor. I also replaced the EVAP canister and valve solenoids. It wasnt until after the rear o2 sensor was replaced that my issue went away. I passed emissions and was happy. I even replaced all the spark plugs and wiring.

About 6 months later during xmas time I went on vacation and left the truck in my garage where rats got into the engine bay and chewed up my windshield wiper fluid tubes and god knows what else. Turning on the truck i got a misfire code. I took the truck in immediately to the mechanic who found nothing and the CEL went away.

Another 3 months went by with no CEL, ODBII showed "Completed" on all diag's. Then I got a P0420 code again.. I reset the CEL and went on my way and had no issues for another 3 months. OBDII again showed "Completed" for all diag's.

Now this week(3 months since the last P0420 CEL). I am getting yet another CEL for P0420 and when looking at the sensor data I show "Rich to Lean sensor" data showing a very high value above threshold, like 175 out of 125 or something. I did not see this 3 months ago when i got the P0420. I drove around for a few days and this sensor data corrected itself and went well below sensor threshold. All sensor data showed green again. I drove around another few days waiting for the CEL to go away and now im showing the same "Rich to Lean sensor threshold" is well above the max allowable value again.

As I stated, Ive already replaced both O2 sensors and the front CAT as well as the entire charcoal canister and valve solenoids for the EVAP system. What else could possibly be the issue here? Is it possible that the rear CAT is no longer enough to keep things in spec and needs replacing as well? The rear CAT is original to the truck and is the only original exhaust part left to change. Any thoughts?

 

The Magnaflow cat will be a high flow unit which is why you are getting a po420 after a while. You could probably use a spark plug fouler thing to keep the PO420 away forever. You can google it. Get the anti fouler thing at oreillys or wherever.

 

Can you elaborate on what the CAT being a high-flow CAT means and why it would be causing the P0420 after a year?

 

AFAIK Magnaflow just makes an aftermarket cat that flow higher than the original cat would. The original cat would cost mucho $$$ from the dealer so a lot of mechanics replace them with ~$100 aftermarket cats. The don't do as good a job as your factory cat of converting the pollutants.

If you've replaced the o2 sensors, which you have, I would suspect the aftermarket cat.

Anecdotal evidence, but I have a high flow Flowmaster cat and it sets a po420 if I've been driving easy for a month or sometimes two.

 

Oh are you saying, if ive been driving light for a while but then start hitting the gas more and driving harder that it might trip a p0420?

 

Actually in my experience it's been the opposite! If I drive easy it trips po420. Higher RPM, more throttle = higher exhaust heat, which is better for catalyst conversion.

 

ah gotcha. So im curious, is it plausible that now that its hot af outside here in AZ.. that it could be contributing to the P0420. I had no issues with the exact same driving conditions all through winter for the most part. I had one incident where it popped up but it went away unlike now where its hanging around.

 

Not all Magnaflows are hi-flow...if you live in CA like I do, then you had to get the CARB approved Magnaflows. I've had mine in for about a year now since putting them on (got the same code which is why I got the new cats) and I haven't had the code come back since, knock on wood.

I wonder how the rear cat is doing...when I got mine replaced my front one was bad but my mechanic told me I should replace both front and rear; he said that when the front goes out, the rear is usually not far behind.

 

That was something i was curious about as well.. hmm, also i did not get a CARB compliant CAT, this is the one i ordered:

$435 MagnaFlow Catalytic Converter 23759: HM Grade, Direct-Fit (EPA Compliant)

https://smile.amazon.com/gp/product/B000XQM2YS/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

 

High flow cat's are what's called 2 - way. What you need is a 3 - way cat. I'm not certain if the CPU can actually detect this or not but in general a 3 - way is going to be more effective all around vs a high flow. Also, some of these trucks use a "heavy metal" cat which basically contains more catalyst material. I can't recall the specifics but I think it was implemented on trucks without EGR.

You'll want to double check the pipe diameter, this is 3" which will not fit stock, I don't know the stock diameter off the top of my head but I used this when I had similar issues and was able to drop the code and also pass emissions which are pretty tight in my state (3 - way sniff test):
https://www.summitracing.com/parts/mpe-99009hm

 

This could not be a catlytic convertor problem at all, it could be a exhaust leak, an air mass sensor etc.
Catalytic convertors react to engine conditions and the maping inside the PCM changes injection, spark etc as a result of the reading from the O2 sensors. If the MAF sensor is flaky, or dirty, the PCM looks at the parameteres for those conditions and adjusts, in short, this is a system of componenets that talk to each other all the time. Get a decent OBDII scan tool and have it monitor long and short term fuel trims. The P0420 code, if I remember correctly is a 2 trip-long term code. Some ODBII scanners will log the data and you can then download the data and look at it later so you arent driving down the road looking at the outputs of the device.

 

@Flowmaster Exhaust

 

thanks dude. i will look into this. Can anyone think of any reason that my computer in the truck would reset itself? All I did was park the truck last night, it sat all night, then i start it up this morning and the CEL is gone. So i check the OBDII status and everything has been cleared and reset, now showing "Incomplete" state as though I unplugged the battery. This hasnt happend that i know of the entire time that i was driving it over the months with no CEL and OBDII showing "Complete" for everything. Almost seems correlated with the fact that it was showing bad numbers and so it maybe reset the entire system to get a clean read? Is that even a thing??

 

If the conditions that caused the CEL are fixed, then the CEL will clean itself after a number of ignition cycles. I'm not sure about the emissions readiness thing though. You should still get a reader and check your LTFT. A cheap dongle and torque app on would do nicely.

 

Oh i do have torque. Ill have to figure out how to read that data you suggested. All ive been watching are the o2 sensor numbers.

 

Let's go back to something that may be getting overlooked. The current issue arose after the rodent damage occurred. Assuming that the replacement catalytic converter, O2's, etc. are fairly new I highly doubt that the newer converter failed while parked for the winter. I took a look at the Amazon link that you posted, and while I'm unfamiliar with the product, according to the details it is a direct replacement based on the OEM specs. This most likely is not a "high-flow" converter. It will have the same/similar cell count to the Toyota original and the system should recognize it as such. You may want to call the manufacturer for additional support. I would scratch the front cat. off of the troubleshooting list as a possible culprit. Same for the other items that have been previously replaced...other than the rear O2. If the rear catalytic converter has failed it most likely has negatively affected the rear O2. It may be on its way towards failure. If you have the means, drop the exhaust and check the rear cat. for blockage or missing catalyst material, that maybe the best place to start your troubleshooting. If rear cat. looks good I would focus on checking the wiring harness for rodent damage. In the end, if you replace the rear catalytic converter I would replace the rear O2 as well. Click on the pic below to learn more about our Flowmaster Catalytic Converter - Direct Fit - 2.25 in Inlet/Outlet - Rear - 49 State, part# 2050005.

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When driving the vehicle in winter time the vehicle may not get to optimum operating temperature which may allow the vehicle's monitors to remain in "ready mode" and not "complete". Once all monitors have been "complete" that is usually when the CEL will illuminate if an issue is present. When the CEL is cleared, all the monitors will reset (which clears the light) but also erases the OBD ECU's memory. Once the vehicle has been through "X" amount of key cycles and drive cycles the monitors will once again be "complete" and the issue will once again arise. These systems do not "reset" themselves; other than the P0456 code which is a "small evap leak" that is usually caused by a loose gas cap.

This is reliable info here, good post!

- Jason @ Flowmaster

 

If the battery had died and the vehicle had to be jump started that will reset the main ECU. Or bad ground or harness issue due to previous rodent damage? These systems will not reset themselves, there's something deeper going on.

- Jason @ Flowmaster

 

thanks dudes. good info again to work from. i agree, something deeper seems to be going on here.. i did check for rodent damaged wiring but couldn't find anything but ill have to check again. very much appreciate the info.

 

If the rodent(s) chewed through an O2 or air/fuel sensor wiring then it would trip this code for sure, I would imagine.