CEL420 Disappearing Act

[fenrisx]

For starters I have a Cali Spec 2000 Toyota 4Runner 3.4L V6(two cats) w 175k miles on the ODO.

Around March or April of this year my CEL came on. I took it to AutoZone and have them scan it, and it came up as the 420 / Catalyst Efficiency code. The light has been on ever since until last week. At one point last week when I started my truck it didn't come on, and hasn't came on since. My granddad said that some trash of some sort might have gotten on one of the 02 censors, and now it's off. I don't know if he realizes how long it'd been on though.

Any ideas on the deal with this? I'm hoping he is right because I don't have the money to have Toyota scan it and figure out the problem, and I definitely don't have the money to have the cat's replaced if that was the problem.

Thanks for any input.

Cody

[Erich_870]

I wish mine would go off on it's own :chair:

There's the remote chance your CEL could have burned out, but mines been on for 3 years so that's probably not it :shake:

Erich

[Obi..]

*At 175k it is likely time that if not done previously, both of your O2 sensors are due for replacement. Yes, possibly a bit of carbon buildup, but that would mean that also you might have some blockage happening with the cat, or the cat was restricted so one of the sensors was getting a dramatically different read than the primary.

Also check for any scuffing to the wire shielding from the sensor to the chassis circuit, frayed or cracking ends at the sensor and connectors, even dirt in the connectors sometimes. Even dirt in the shielding will eventually wear into the wire covering causing a short if there's any dampness or moisture present.

Weather pack connectors take a lot, but they're not 100% bulletproof, especially with that many miles with whatever amount of play and off roading mixed in. :thumbup:

[fenrisx]

Thanks for the info. Hopefully the light doesn't come back on and I can put this as 2nd in line on my list of things to do (timing belt/water pump being first).

[fenrisx]

Well the light is back with a vengeance! My wife left to come pick me up at school and said the car was making a loud noise when she pressed the gas, and felt funny. Then the light came back on as well.

Oh well... :(

[MTL_4runner]

Replace the sensors first before doing anything else to it.
Try to check for an exhaust leak before the sensor which might also cause this code.

[Erich_870]

Bummer :(

I finally found my scanner after MONTHS of searching. It was under a tub of baby cloths destined for long term storage in the shed. Anyway, I turned off my CEL and I'm plesntly surprised that it's still off. Sadly my MPG has not gone up. :loser:

Erich

[Okie81]

So it only happened when you wife drove it?

If a sensor replacement doesn't work, you may need a new cat, or a new wife (j/k) :D

[fenrisx]

I won't be able to get it fixed until the first week of February, and that can't come soon enough.

Aside from it being super loud now, and the exhaust smelling a lot worse, the 4Runner is going through gas extremely quick. About 50 miles on a full tank and it was sitting at half a tank.. another 15-20miles of driving and I'm 1/4 tank.

[fenrisx]

I figured I'd update this thread... a year later.

When the CEL returned it wasn't the PO420 I don't think. I didn't run it again to find out. The cause of the loudness was the rear O2 sensor had blow off, and was hanging by its wire. The cause of the worse than shit mpg was due to the air/fuel sensor(?).. I'll have to double check that with the receipt.

Toyota Stealership replaced the faulty air/fuel sensor, re-threaded the holes for the rear 02 sensor, and put it back on. Cost to me was a bit over $500(including Corolla rental for a day).

Had it not been a snowy winter, with a newborn, and full time work/school, I'm sure I could have saved myself about $500 and done this myself.