0420 Code Catalytic Converter

[quatin]

I had my Cat stolen 2-3 years ago. I had a muffler shop weld on an aftermarket cat. Now, almost a year later, I'm getting the check engine light for "low catalytic converter bank 1". I'm being told it might be my O2 sensors going bad, but I had them read with a computer and the waves look ok. However, the check engine lights only comes on every couple of weeks.

Anyone else go through something like this? I might end up swapping out the O2 sensors anyways, since they're originals.

 

[mikebontoft]

I thought that code is supposed to be "catalyst efficiency below threshold."

what voltage did the rear sensor actually range from as opposed to the waves just looking "ok?"

I guess after reading the codes, it gets cleared and you drive it for awhile? It probably just takes awhile to finally complete a drive cycle for the emissions system self test before finding the efficiency out of spec.

 

[quatin]

I don't remember what the exact levels were, but we had the O2 sensor spec in front of us and the voltage swing was within boundaries.

We would reset the code and run the engine while watching the O2 sensor readouts, but the light never came back on. It would take some 200 miles before the light would come back on again. Sometimes the light turns itself off after a day or two before I get a chance to have the code read again.

 

[mikebontoft]

That was the rear sensor, correct? If so, then I could see an intermittently failing sensor a possibility. The cat itself either works or doesn't (yes, I know it can wear out... but my point is that it's not going to be dead one day and work great the next). You may want to observe the front sensor(s) as well. A change in the air/fuel ratio will affect how the cat operates and could potentially be the cause as well.

 

[TheDurk]

I don't remember what the exact levels were, but we had the O2 sensor spec in front of us and the voltage swing was within boundaries.

We would reset the code and run the engine while watching the O2 sensor readouts, but the light never came back on. It would take some 200 miles before the light would come back on again. Sometimes the light turns itself off after a day or two before I get a chance to have the code read again.

The drive cycle required for completion of the cat test is quite involved and requires a minimum of 2 trips--but usually takes more than half a tank of gas. Details here:
Toyota TSB courtesy IH8MUD

 

[quatin]

We did check the front sensor as well and everything seemed to be within the limit lines. My MPG was also very steady when all of this was happening.
I did run some Seafoam through the vacuum lines and the gas tank and the light didn't come back for 2-3 months. However, now it's coming on and off every other week. I've saturated both sensor mounts with PB blaster in anticipation of replacing them. Should I replace both? Any particular aftermarket o2 sensor have high recommendations?

 

[TheDurk]

We did check the front sensor as well and everything seemed to be within the limit lines. My MPG was also very steady when all of this was happening.
I did run some Seafoam through the vacuum lines and the gas tank and the light didn't come back for 2-3 months. However, now it's coming on and off every other week. I've saturated both sensor mounts with PB blaster in anticipation of replacing them. Should I replace both? Any particular aftermarket o2 sensor have high recommendations?

You want the OEM Denso sensors. Check prices at Amazon and rockauto.com. Get the Denso part numbers here: http://www.densoaftermarket.com/catalog/

You should probably do both if they are indeed original. Do the rear if you just do one. A new front may show an improvement in mpg and performance even if it does nothing for the P0420.

 

[quatin]

You want the OEM Denso sensors. Check prices at Amazon and rockauto.com. Get the Denso part numbers here: http://www.densoaftermarket.com/catalog/

You should probably do both if they are indeed original. Do the rear if you just do one. A new front may show an improvement in mpg and performance even if it does nothing for the P0420.

Thanks.

Also, are both sensor before and after the Cat O2 sensors or is the front one an Air/Fuel ratio sensor?

 

[TheDurk]

Thanks.

Also, are both sensor before and after the Cat O2 sensors or is the front one an Air/Fuel ratio sensor?

Front is O2 on '98 and earlier and 49-state Federal '99-'00. Wideband A/F on '99-'00 Cali. emissions and all '01 and later.

All rears are o2.

 

[T4R_Finally]

My understanding is that only the downstream sensor will throw the 0420 code. I was getting that code right after I bought my 3rd gen and I reset it a couple of times and it always came back after a short time. I put a new denso sensor on it and haven't had any cel since and that's been well over a year now. According to service history, the upstream sensor had already been changed so I didn't replace that one.

 

[TheDurk]

My understanding is that only the downstream sensor will throw the 0420 code. I was getting that code right after I bought my 3rd gen and I reset it a couple of times and it always came back after a short time. I put a new denso sensor on it and haven't had any cel since and that's been well over a year now. According to service history, the upstream sensor had already been changed so I didn't replace that one.

Not totally true. Here is the list from the FSM of the causes of P0420 codes:

Gas leakage on exhaust system
A/F sensor (bank 1 sensor 1)
Heated oxygen sensor (bank 1 sensor 2)
Three-way catalytic converter

http://tacoma.site40.net/4Runner_96-02_Repair&Wiring/techinfo.toyota.com/ileaf/02toyrm/02toypdf/02rmsour/2002/024runne/di/eg5vzfe/cip0420o.pdf

It IS true that the rear sensor has nothing to do with any code other than P0420 and its own fail codes, but the front sensor can contribute to the P0420--it just usually sets other codes first or at the same time. After all, the code is generated from a comparison of the two sensor outputs.

 

[fish0281]

If I were a betting man, is say your 1-year old cat is not performing to what the ecu deems acceptable. The aftermarket cats are hit or miss and there is a reason they're much cheaper than a Toyota-sourced one, usually because the catalyst materials (precious metals) aren't up to snuff.

That being said, I wouldn't be surprised if it passed an emissions test anyway. I'd get the URD sensor thing and be done with it.

 

[BlackCat914]

you not only need to be concerned about the voltage swing of the readings, but also the speed at which they're varying.

 

[tee-bone]

FYI, I have/had what appears to be the exact same symptoms.

Code P0420 getting thrown intermittently. Sometimes it happens every tank or two. Sometimes it goes three of four tanks without it happening. Sometimes it happens multiple times in a row, every 50-100 miles.

I just clear the code. My mileage has been decently consistent, and I have yet to fail an inspection. Perhaps if you bought a ScanGauge or the equivalent so that you can easily reset it yourself (plus you'd get the other benefits, most notably trans temp) it would be something you could just live with.

 

[quatin]

I went and bought the Denso OEM style and the cables were 4'' too short. I double checked the part number to Denso website and it's the correct part. It looks like I'm going to have to get the universal style so I can splice the cables. However, is there a difference between the RWD and 4WD part? The Denso website lists it as the same part, but at Autozone, it's different.

I'm in Florida, so I don't even have emission testing. I'd just like to solve the CEL in case a real problem shows up.

 

[TheDurk]

I went and bought the Denso OEM style and the cables were 4'' too short. I double checked the part number to Denso website and it's the correct part. It looks like I'm going to have to get the universal style so I can splice the cables. However, is there a difference between the RWD and 4WD part? The Denso website lists it as the same part, but at Autozone, it's different.

I'm in Florida, so I don't even have emission testing. I'd just like to solve the CEL in case a real problem shows up.

We can't help you with part numbers if you don't tell us what you are driving: year, engine, trans, 4x4 or not, Cali. or Federal.

 

[quatin]

We can't help you with part numbers if you don't tell us what you are driving: year, engine, trans, 4x4 or not, Cali. or Federal.

2000 Base 2.7l RWD Automatic, Federal (at least I think it's federal since I didn't buy in California)

 

[TheDurk]

2000 Base 2.7l RWD Automatic, Federal (at least I think it's federal since I didn't buy in California)

That's probably your problem. Cali. 4Runners were sold all over the US in 2000, probably more Cali.'s than Federals even outside Cali. itself. I bought my '99 Cali. new in New Jersey. Climb under it and count cats. Two cats = Cali. emissions. You can tell from the emissions label under the hood, but those can be mis-leading.

I bet you have a Cali. and thus bought the wrong part.

EDIT: That's weird. Denso shows both the 234-4154 and the 234-4162 as the downstream OE type sensor for that application, for Federal Emissions. Which did you get? The 4162 is 10.6" wire length and the 4154 is 12.9".

On the 2000, you should check if you have the flanged or screw-in rear sensor. Denso shows both.

 

[mikebontoft]

A better way to know is to pop your hood and look at the underhood emissions label, likely on the hood itself.

It will say something like "This vehicle conforms to model year 2000 US emissions blah blah blah and California emissions" or something like that. I honestly haven't looked at one for awhile since I've been out of the repair business for a few months.

 

[quatin]

I bought the 4162. I'm pretty sure it's a flanged type, it has the diamond looking bracket that the bolts go through.

I only have 1 cat. Under the hood it says.

"THIS VEHICLE CONFORMS TO US EPA REGULATIONS APPLICABLE TO GASOLINE-FUELED 200 MODEL YEAR NEW LIGHT DUTY TRUCKS PROVIDED THAT THIS VEHICLE IS NOT SOLD OR DELIVERED TO AN ULTIMATE PURCHASER FOR PRINCIPAL USE IN THE STATE OF CALIFORNIA OR A STATE THAT HAS ADOPTED CALIFORNIA STANDARDS UNDER THE AUTHORITY OF SECTION 177 OF THE CLEAN AIR ACT AND THOSE STANDARDS ARE IN EFFECT"