Help: P0420 code

[Ray]

I have an 01 Seq. Limited, 128K miles. Definition P0420 - catalyst system below threshold bank 1. Any idea? O2 sensor? Cat? Bank 1, driver/passenger side? Before/after cat?

My MIL: P0420
Pending: P0420

Freeze frame data below
RPM: 1344
Load value: 32.9%
Coolant temp: 179 F
Intake air temp: 51 F
Short term fuel trim 1: 0.0%
Long term fuel trim 1: 14.8%
Short term fuel trim 2: 0.8%
Long term fuel trim 2: 11.7%
Short term fuel trim 3: -100.6%
Long term fuel trim 3: -100.6%
Short term fuel trim 4: -100%
Long term fuel trim 4: -100%
Speed: 21 mph
Fuel system 1: closed
Fuel system 2: closed

[RogueRider]

Bank 1 is left (driver side). I don't know how to read the freeze frame data to isolate the problem, sorry. The P0420 DTC could be the cat, O2 sensor 1 or O2 sensor 2. I had the same code and it turned out to be the cat but you'll want to make sure its not an O2. My friend owns an auto repair shop and he put the #1 and #2 O2 sensors on the diagnotic screen while we drove around (I drove, he watched the screen) to determine that the O2 sensors were functioning. The O2 sensors were not dead so we replaced the cat. Another way he troubleshoots the problem is to move the O2 sensors to the other bank and see if the DTC switches sides. Not a simple task but if you don't have a diagnotic tester to look at O2 wave forms.... PM me if you want more detail on the diagnotic waveforms.

[JBH1989]

Can you post the sensor values for the oxygen sensors?'

Fuel trim for 3 and 4 look WAY off. It's saying that 3 and 4 are running EXTREMELY rich.

You have three main causes for the code, the H02S, the catalytic converter, or a leak in the exhaust. Judging by your fuel trim, it's most likely in the sensor.

Has any other work been done on the vehicle?

It might be time to get a real diagnosis done on it though, one way or the other something is not right and it could end up being very bad. If it's leaning out the engine that much, it could damage it.

[Ray]

Thats all the data that shows on my OBD scanner. Due to mileage I think I will just change my O2 sensor. Also, there was no work done in the vehicle.

[jliltd]

Good idea. Replace all 4 O2 sensors if you want to shotgun it (I assume you will do work yourself). It is extremely rare for a catalytic converter to go bad within 200,000 miles and they are very expensive. And O2 sensors in these motors are known to go bad with regularity. I have been to two different dealers who swore the cat needed replacing when it was only an O2 sensor after all.

If you want to save some time/money then just replace the two O2 sensors for Bank 1. Stick to the Denso brand sensors (OEM supplier to Toyota). I think I bought two from sparkplugs.com that were OEM and two more that were aftermarket Denso. Don't buy Bosch sensors for a Toyota no matter what compatibility is claimed by Bosch.

Here's a post I made about replacing the O2 sensors on an '01 Sequoia with a lot more detail:

Oxygen Sensor Part Number and Location

[Ray]

I will doing the work myself. Just receive Denso O2 sensors (manifold and after cat), and catalytic converter (bolt on, one piece, flange, pipe) for Bank 1. I will just do Bank 1 for now.

[JBH1989]

Why are you replacing the cat?

[jliltd]

I'm with JBH on this one. Keep the new cat in the box so you can return it. If after you change out the O2 sensors and clear the codes you may well find you don't really need to change the cat, saving lots of effort and money.

[Ray]

I replace the cat because when I tested the O2 sensors on the car with a scan tool and bench tested them, both sensors are working properly. I'm keeping the cat for at least two weeks, about 400 - 500 miles running the new cat. I bought the parts at rockauto, cat with pipe $240.

[JBH1989]

Are you basing it on voltage range of the sensors? They did exceed 800mV and below 450mv?

I wouldn't open the new cat (can't return an open cat usually) unless I knew absolutely for sure that it was the cat and not the sensors (ie run the new sensors for a few drive cycles and see if P0420 comes back). Then again I hate shotgunning a vehicle with parts.

Cat's don't commit suicide--they are murdered. They don't just go out, either something was really bad that you ignored (like a flashing CEL but you didn't post any misfire codes). Any sort of catalyst damaging event would have triggered a CEL and set multiple DTCs. H02Ss on the other hand do go bad with age routinely--the heater more often than the sensor in my experience.

[Ray]

I used a scanner (borrowed) that can read O2 sensors waveform and the bench test using a blow torch the tip of the O2 sensor and monitor the output voltage. Also, I had that rotten smell from the exhaust.

I didn't have any misfire but I had an exhaust manifold leak for awhile that I ignore (fix). Thats the only code (P0420) that ever appears since I own my vehicle.

[JBH1989]

Did the H02S peak over 800mV and below 450mV?

[Ray]

The HO2S peak above 800mV and below 450mV.

[JBH1989]

Okay, just checking because you can get a good sensor waveform with bad sensors.

[sequoiasoon]

Dealer just replaced my cat for the same code. Had gone in before and they replaced the O2 sensors but code showed up again. Covered under factory warranty for emmisions.