Need advise on Code 420 Catalytic system efficency below threshold.

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Mike G

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Traveler III

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San Jose, CA
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Need advise on code 420. A few months ago my CEL came on and I checked the code to be 420, "Catalytic system efficiency below threshold". So I'm guessing it was a bad O2 sensor. I was going to order a new O2 sensor today but on Friday I noticed the CEL light is no longer on? The only difference I can think of is I just filled up my tank with 76 gas and normally I use Exxon or Shell. Could it of been the gas I was using? The 4Runner has 162K miles on it and it runs great. No issues even with the CEL on and gas mileage never changed. Should I even bother to change the O2 sensor? I know its about time I should, especially with 162k miles on it. How long do O2 sensors last anyway?
 

WJ - Firefly

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A loose gas cap can also cause this code. When changing sensors, the front sensor is usually the one out of spec.
 

ecco

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I had this code pop up on my runner at high elevation a few months back. I ended up resetting it and it never came back on. If your O2 sensor has never been replaced I would do so anyway. I changed mine for what I think was the first time at 174k and it definitely made a difference.
 

VCeXpedition

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It could actually be your Catalytic Converter.
Here's what IH8MUD has on that code:
--> P0420: Catalyst system efficiency below threshold: Trouble Areas: Three-way catalytic converter; open or short in heated O2 sensor circuit; heated O2 sensor.

It could be the heated O2 sensor or circuit, but there's ways to check that and that would be a different code.
--> P0135: Heated O2 Sensor Heater Circuit malfunction (Bank 1 Sensor 1): Trouble Areas: Open or short in heater circuit of heated O2 sensor; heated O2 sensor heater; ECM.

If you're not getting both codes, I would suspect the Cat itself, which is unfortunate because they're a little pricey, especially if you live in California, I know firsthand. I ended up replacing the cat on a '98 Tacoma for a Po420, but it had 209,000 miles on the original cat.

The good news is, if you're not selling it, you can reset it and it will likely not come back quickly. If it does come back right away, it might pay to have a smog check done to see if the cat is actually good or bad.

g'luck, Dan.
 

stoney126

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I believe a loose gas cap would give you a po455 large evap leak code.
How long weRe you driving before it went out?
What did you use to check the code? Does it show how many good trips since it set?
Hate to waste money on 02 sensors when it's a fuel trim issue
 

stoney126

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Napa Ca
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It could actually be your Catalytic Converter.
Here's what IH8MUD has on that code:
--> P0420: Catalyst system efficiency below threshold: Trouble Areas: Three-way catalytic converter; open or short in heated O2 sensor circuit; heated O2 sensor.

It could be the heated O2 sensor or circuit, but there's ways to check that and that would be a different code.
--> P0135: Heated O2 Sensor Heater Circuit malfunction (Bank 1 Sensor 1): Trouble Areas: Open or short in heater circuit of heated O2 sensor; heated O2 sensor heater; ECM.

If you're not getting both codes, I would suspect the Cat itself, which is unfortunate because they're a little pricey, especially if you live in California, I know firsthand. I ended up replacing the cat on a '98 Tacoma for a Po420, but it had 209,000 miles on the original cat.

The good news is, if you're not selling it, you can reset it and it will likely not come back quickly. If it does come back right away, it might pay to have a smog check done to see if the cat is actually good or bad.

g'luck, Dan.
Ya if it was a bad heater the cel would be on all the time since there would be an open.

Wonder if there is a pcm update. Go to the dealer at all?
 

Mike G

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San Jose, CA
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Today I changed both O2 sensors, cleaned the MAF sensor, and I also replaced air filter and the gas cap. The gas cap was just $25.00 so I thought it wouldn't hurt to replaced since the original cap is about 13 years old. Hopefully this fixes the PO420, I hate to buy a new Cat!
 

Mike G

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Traveler III

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San Jose, CA
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I believe a loose gas cap would give you a po455 large evap leak code.
How long weRe you driving before it went out?
What did you use to check the code? Does it show how many good trips since it set?
Hate to waste money on 02 sensors when it's a fuel trim issue
Was driving about 100 miles before the CEL light went out. But when I was driving home the next day, it came back on. Same 420 code and I used a friends OBDII meter to confirm the code. "Does it show how many good trips since it set?" Didn't check that part.