P0420 is back

[T4R_Finally]

When I first got the 3rd gen, I was hit with a CEL and a P0420 code. Long story short, I installed a new Denso rear O2 sensor and the code never came back. Have since gotten a CEL with a MAF sensor code - cleaned the sensor and no issues since. The P0420 was over 2 years ago. My daughter is on her way home for spring break - 5 hour drive, so I'll be interested if there was any noticeable decrease in mpg indicating a possible bad cat situation. If not, is it likely the sensor again, after just 2 years? Would it do any good to pull and clean that sensor or is that pointless? She'll be home with the 4Runner for a week or so, so I'm hoping to get it resolved while she is here.

 

[TheDurk]

I'd just clear it and see what happens. Maybe check closely for exhaust leaks as flange bolts and gaskets can rust out. As our trucks age, our cats are closer to the efficiency limits and rare adverse conditions can provoke spurious P0420's. I got a P0420 last summer driving slowly for 40 minutes through a park with a 20mph (strictly enforced) speed limit. Hasn't come back. P0420 is only a big issue when you have to pass inspection or you have a really plugged cat.

 

[jgue467]

I get it too (p0420)

from time to time. I clear it goes away for 1-2K miles. I know what's causing mine. Like TheDurk said, exhaust leak at one of the flanges near the front. My otherwise good mechanic replaced my cats and didn't re-use the flanges, put the ones that came with the aftermarket cat. So now after taking it back 6 times (each about 3-5 months apart) its doing it again, minor leak, i can hear it and so does the puter. I took it to an exhaust shop, they said take it back to mechanic, he messed up with aftermarket flange, they one he used just won't work they said, will do it over and over. Its a hastle to take it to mechanic, have to drop it, get a ride to work and vice versa. I almost am ready to find the leak myself and just lather it with jb weld. thoughts? how much worse could that make it?

Ok now to try to help with your issue. The 0420 code is saying there is not enough of a difference between the readings taken from the front and the rear 02 sensors. Meaning either the cat is inefficient, 1 or both sensors are bad (not likely), a leak towards the front of the front sensor (making it so its reading is off). So go from the cheapest to more expensive solutions. When the code trips on mine, it does not affect fuel efficiency. But I do not like how toyota then turns the safety features off (to save the engine some power if needed), plus of course the cel light, errrrr....

Here is some info I found on the code that may help with technical diagnosis (some mentioned already but wanted you to see the whole thing:

P0420 Catalyst System Efficiency Below Threshold (Bank 1)
HO2 sensor after the catalytic converter is not responding normally.

1. Check for leaks in the exhaust system between the engine and the cat converter (loose connection, rusted area, or burned out seal)

2. HO2 or A/F ratio sensor before cat converter is bad (remove connector and measure resistance between terminals +B and HT - should be 0.8-1.4 ohms cold).

3. HO2 sensor after cat converter is bad (measure resistance as above - should be 11-16 ohms cold).

4. Cat converter is bad.

If you need to replace a sensor, bring your VIN to a Toyota dealer and get the correct part number for your engine. There is only one that works correctly, but at least two available. You don't have to buy the part from Toyota, but you have to have the correct part number.

Good luck!

 

[T4R_Finally]

Okay, this could be either possibly issue I guess but Durk may have hit on something. A couple of weeks ago, I took the family up to the mountains where she goes to school, for a little snowboarding. We rented a house near the resort, which means we were near the top of the mountain. The night the CEL came on was when she left the house we were renting to go back to her apartment on campus and the snow melt was icing back up in patches on the roads - so she had to drive slower than usual, was getting a lot of wheel spin in spots, and then the extra stress on the truck of going up and down steep grades. That night, she called to say she made it back home okay but the CEL had come on.

She got here last night, the CEL is still on but there was no noticeable difference in mileage or anything else. I can and will clear the code first and we'll just see if it comes back. Problem is, it won't get driven much while she is here. If it's going to come back on, it will probably be when she's on her way back to school. But if it's not hurting anything, I may just send my code scanner back with her so she can check and clear it herself just in case a code comes up for something else. I'm not big on driving around with the CEL lit on a 14 year old vehicle and assuming no other codes have come up.

If it does come back, I'll just deal with it over summer break. Will have it checked for leaks and move on from there. I find it hard to believe the sensor itself has failed after just 2 years.

 

[jgue467]

Interesting under what conditions you got the p420

when i think back i get mine under similar situations. Not mountain climbing but driving slowly offroad (5-10) thru a fair amount of packed, loose soil and rocks so the tires will slip here and there even in 4wd. Yeah it doesn't affect fuel efficiency or engine performance but I don't like that it turns traction control Off, that is really somewhat of a safety hazard not having that. I can handle it but i wouldn't want anyone else driving it that isn't aware of those safety features missing. Good luck!