P0420 check engine light. Upper cat at fault or sensors, etc?

On My 2001 Tacoma, V6 3.4L - The P0420 Check engine light has come on.

On the highway when I reach around 50 MPH or so I notice that the truck starts acting a little weird and seems to struggle a little, loosing power and seems to be struggle to keep up with that speed.


Otherwise the truck performs great on speeds leading up to that. I do see some slightly thicker smoke coming out of tail pipe but its been like that for awhile. I havn't changed to spark plugs in several years and part of me thinks this may be causing my engine to send some un-burnt fuel to the exhaust, not sure.

I did try a sea-foam treatment though the vacuum lines but that didn't seem to help, although the check engine light did come off I am sure it will return.


I am pretty sure I need a new upper cat. I had an aftermarket one put in 6 years ago so I think it might be time to be replaced just not sure if it could be a sensor or something else. My rear cat is original to my vehicle. I did do a temperature test for the upper cat and the intake temp is 345 degrees F and outake is 218 degrees F

In addition My OBDII reader which is an INNOVA model# 3100 f device - which uses a site called "repairsolutions.com" has given me these stats:




If I bring the truck into a mechanic to get diagnosed should I have them focus on something in particular that they might overlook? Just want to rule things out. I really hope its just the upper cat.

 

"I am pretty sure I need a new upper cat. I had an aftermarket one put in 6 years ago so I think it might be time to be replaced just not sure if it could be a sensor or something else. My rear cat is original to my vehicle. I did do a temperature test for the upper cat and the intake temp is 345 degrees F and outake is 218 degrees F"

Are you saying you measured the exhaust pipe before the upper cat and after the upper cat and those are the temps you got?
If so I would lean towards a bad cat. those temps seem like its slightly clogged. The seafoam would trick the O2s, whether it was a cat or a sensor issue.

Yours being a V6 I assume you have 2 upper o2s and 2 lowers? you could try swapping the the o2s right to left and see if the code changes sides. If so its the O2 sensors if it stays the same go for the cat.

If it is the Cat I would change the Spark plugs at the same time as they could be the reason your cats are dyeing so soon.

 

a long explanation so hang in there. The P0420 code is telling you that your catalytic convertor(s) are not functioning properly. This could be due to an exhaust leak, worn out cats or bad o2 sensors / AF sensor. The general explanation for o2 sensors is that the front o2 sensor senses the rich - lean running of the motor by a small DC voltage signal. a .5 volts DC is perfect air/fuel ratio but it is constantly adjusting from a low of .1 volt dc to .9 volts. This gives a saw tooth wave form signal to the PCM. When the cat(s) are functioning properly the rear o2 sensor should have a relativity flat wave form... the cat(s) are storing o2. When the cats are questionable the rear wave form will look like the front wave form and when this happens enough, the check engine light is illuminated. When the CEL is on, the PCM uses a default "map" for controlling the injection and the ignition. If the PCM senses via its various sensors that there might be engine damage the CEL will flash and if this continues it will shut the truck off. A decent shop can check the signals from the sensors.

As to your question... have them check for exhaust leaks first. They can either put some rags over the tailpipe, restrict the flow and listen for the hiss or they can smoke test the exhaust. If no exhaust leaks are found, check the o2 sensors. They should be able to do a propane enrichment test to see if the 02 sensor(s) react and how fast they react. This will either confirm that the o2 sensors are functioning and it indeed needs cat(s).

 

thank you thank you i am going to mention that propane test and testing for exhaust leaks , thats very interesting

 

P0420 is rarely anything but a cat, exhaust leaks should be heard, especially on cold start. The upper cat located between the upstream and downstream sensors is the only one monitored.

Aftermarket cats are hit and miss and you very likely need a new replacement.

 

"Are you saying you measured the exhaust pipe before the upper cat and after the upper cat and those are the temps you got?
If so I would lean towards a bad cat. those temps seem like its slightly clogged. The seafoam would trick the O2s, whether it was a cat or a sensor issue."


ANSWER: Yes thats correct, this is the temp difference before and after intake of the upper cat. One other way I heard to test for clogged cat would be to unplug an 02 sensor from exhaust manifold to let exhaust escape. If performance and acceleration improves this is a result of a clogged cat???

 

And there is a popular video by Scotty Kilmer, who I love, who claims pouring a gallon of lacquer thinner in your gas tank, at half volume, then refilling at 93 octane and driving at high RPM for around 150-200 miles is a good way to clean a cat. Trust me, it tempts my mind to do that but I don't want to melt any plastic components. LOL - still some people report getting good results!! If only it were that easy?!


- prerunnerSD
DIVESUMMIT

 

I've had that code several times. It's always been an exhaust leak.

 

But why would an exhaust leak cause the truck to hesitate, have trouble to accelerate beyond roughly 50MPH, seems more related to RMP not just sped but being at sea level it seems to be around 50mph??? That seems to be caused by a clog. There may be a leak but the performance is most what I am worried about. thanks anyway for the input i'll mention that and try to see if this is happening

 

if you live in a "smog state" your hand is going to be forced and if it needs cat(s) you are going to have to put them on. By letting the exhaust out the O2 sensor hole you are giving the exhaust a place to go other than through a partially plugged cat. Plugged cats can be tested on the lift or if you are handy you can take the cat(s) and exhaust off an look.

There is an alernative. URD, a vedor on TW, sells a rear o2 sensor simulator. It plugs in between the rear o2 sensor and the PCM and smooths out the saw tooth signals to the PCM. I have 2 of these on my 2 Tacomas that are in Cabo San Lucas. Thousand and thousands of miles on these vehicles with zero issues. If you live in a smog state and get caught with this installed, you are in trouble with the states "smog police".

Unfortunatly in the auto repair world there has been a tendency for auto techs to turn into parts replacers and not diagnosticians. A mis-diagnosis of the P0420 on your truck could cost you thousands of $ - factory cats are $$$. If you look at an aftermarket cat for 1/2 the price you will see that there is 1/2 the actuall working material inside. You get what you pay for.

 

+1. I have the URD installed on mine with a straight pipe for at least 10 years now, after my converter was stolen. Limited issues but have had to replace both O2 sensors. Recently got a 420 code a couple of weeks ago, cleared it and will wait and see. If I could find a good converter at non dealer OEM price I would replace the straight pipe. But I have heard thefts are again on the rise, so what to do???

 

Update: All it needed was a tune up with new spark plugs. The p0420 code was coincidental to the performance issues. Where the truck was shuttering and having struggle to accurate on highway, I had a gut feeling this was the case.
A mechanic that was recommended to me on here did a test drive and live data scan and figured out there was a misfire in the fourth cylinder.

Its clear I will likely need a new cat or sensors but I was misguided by my first mechanic who I paid a "diagnostic fee" who didn't even catch the misfire.

Coincidentally the first mechanic said my downstream 02 sensor was running at less than 1 volt so I am still researching that but at least for now my truck is running well. I am going to get a infrared thermometer and record the temperature values before and after cat to get more info on if they are getting hot enough.

Glad I didn't start throwing new cats and sensors into the exhaust system, it pays to get a second opinion!

- prerunnerSD
DIVESUMMIT