Intermittent CEL (P0420)

[digital022]

Hi all,

I have been experiencing an intermittent CEL for quite some time. I had the codes checked when the CEL went on initially and according to the guy at Pep Boys it was giving a P0420 that was showing up twice. No idea if this refers to the front and rear o2 sensors being bad. Anyhow, the CEL eventually went off by itself and ever since the CEL has gone through cycles of being on and off every few hundred miles.

I thought this would be an issue when it came time to pass smog. However, when I took my 4runner to get smogged the CEL was off and it had no problems passing smog.

The CEL recently came on again and I am noticing a lag and power loss. I haven't kept a close eye on MPG but I'm sure that has taken a hit as well.

I'm hoping that replacing both o2 sensors will resolve the intermittent CEL but I'm wondering if there are any underlying issues that may be causing this to occur, and whether its the sensors at all.

Any ideas on why this may be happening?

I have a 99' 3.4 V6 by the way.

Thanks

 

[TheDurk]

Well, I would certainly pull the current code to see what it is. Failing to pull a code and then asking the internet what the problem is equals a very dubious approach in my book.

The most likely underlying issue is whatever code you aren't looking at. Second are the sensors themselves. Third would be any exhaust leak, however slight, between the engine and the rear sensor.

 

[jgue467]

Catalyst System Efficiency Below threshold bank 1

Possible causes:
1. Gas leakage on exhaust system (several places this can happen before and after 1st cat.

2. A/F sensor (bank 1 sensor 1)

3. Heated oxygen sensor (bank 1 sensor 2)

4. Three-way catalytic converter

Find the tech manual to instruct on how to perform tests on #2-4. Mine does it occasionally also, its #1 in my case. Working on it... Luck! :banana: