Another Check Engine Light Problem

The car is an '04 Toyota  Matrix XRS. Yep, the 2ZZGE 6 speed. Just over 100K miles. Here's the somewhat lengthy story:

It tripped error code P0420 a while back. I made a "test pipe" to get me through a while. Popped the same code.

I put on a new cat, O2 sensors, replaced plugs, PVC valve, air cleaner, radiator (unrelated to CEL), and anti-freeze.

Now it is giving me the same error code.

I bought a cheap "non-CARB" cat from Amazon. It did not have a flow direction, so I guessed. Could it be in backwards? Could it just not be effective enough to show a difference between the two O2 sensors?

I may have my two O2 sensors reversed. I pulled them from the package thinking I could tell the difference by the wire configuration, but unlike the originals, the wires, grommets, etc, allow them to go in either position. I reversed them once already, but believe I'll do so again, as lots of stuff has changed while I've been chasing this CEL (I had a vacuum leak that triggered a IAC code, but got that sorted). I could also put the original 02 sensors back on in what I can confirm is the correct position.

I also replaced a battery terminal, and cleaned up the connections on some You Tube advice I thought couldn't hurt.

Today, I'll change the sensors, and clean the throttle body as best I can, but would appreciate any other advice the brain trust might have. 

One Sensor has holes like an old aircraft machine gun, like so,

the other has far fewer. Like one row. Anyone know which one should be pre-cat?

P0420 is a pretty specific code that means your rear oxygen sensor is seeing the same reading as the front one (no change.) it really can’t be caused by much other than a bad converter in my experience.

I’d guess your converter isn’t doing much.

I doubt the sensor position would matter. If they both plugged in, they’ll get a reading, and it’s comparing the front to the rear. 

I read somewhere about putting an anti fouling tip like used on a spark plug in an engine that burns oil can work to fool the system.  Basically take the sensor out of the stream.

Non foul mod

What does a factory cat cost?  I understand that it is an 2004 car, but is this headache worth it?

noddaz

Cat prices are directly proportional to the amount of active ingredient (Platinum) contained.

If you monitor your rear O2 sensor voltage with an OBD scanner, it should remain constant, while the front O2 voltage oscillates.  

If it doesn't, the cat isn't working.

For holey vs non-holey O2 sensor positions, I'd hit Rock Auto and look at pictures.

Did they have OE style connectors or were they the universal type you wire yourself?  Usually takes several drive cycles to trigger P0420 if you have a marginal cat, so something my be wired wrong.  Look at O2 voltages to see if the ecu is getting expected inputs.

In reply to cdowd :Oooh, Thanks for that!

Thanks all for advice.

To answer some questions, These are nice, expensive Bosch sensors that plug directly in as if stock. The cat and pipe is like $400 bucks, and I am already regretting cheaping out. The nuclear option of a new complete exhaust for near a grand is looming. I really don't want to spend that much, but it may be the way. For $6 and change, I tried the fix from Cdowd's video. FWIW I live in a non-MARTA county, I just don't want to get used to driving around with a CEL on, in case it is trying to tell me something important.

The one time I tried the O2 spacer thingy it worked as advertised. It's certainly worth the $6 to try it and it's a good trick to know. 

Tyler H said:

Cat prices are directly proportional to the amount of active ingredient (Platinum, Palladium, and Rhodium) contained.

 

FYP.

Wheelsmithy- I agree that it's the cheap cat that's the source of your light.  It may be so cheap that the anti-fouler trick may not even work.