CEL/MIL P0420 - way to test O2 sensor? - aftermarket cat?

[Sella Turcica]

So at 107k miles my 2.4L '03 CEL came on. Code read as P0420, "bank 1 catalyst efficiency below threshold". The light subsequently went out a few hundred miles later, came on and went off again. I assume it will be back soon.

So, I gather from reading that it's most likely a bad front cat (this is the one in the manifold, right?) and less likely to be the O2 sensor (which one?). A couple of questions: I have a multimeter and some ramps, is there a way to definitively see if it's the O2 sensor without replacing it? I've seen people mention this but without a specific DIY method. Are the aftermarket cats ok? Places like rockauto and authaus az have them for <$400. I can certainly install one myself, provided they are bolt-on and I don't have to do some special ECU reprogramming.

Thanks guys

[somick]

There is a TSB No. EG013-04.

Recalibration of the ECM may work.

Good luck,

Sam

[gdanaher]

I'm not an expert on this topic so consider the source. If I recall the O2 sensor continuity should approach zero when cold and new. Using your ohm meter, check the sensors when the engine is cold and see if you see a value indicating high resistance, or even an open. If in doubt, check all sensors and note the measured values. Check at the parts store and measure the value of a new generic sensor for purposes of comparison.

[darksparkz]

Bank 1 is pre cat I believe.

[joshuaboston]

Had this code with my last car.... it was the 02 sensor. I would not go with a OEM CAT unless you are 100% sure it is the CAT.

A OEM cat will never be as good as one from Toyota and the cost between a OEM cat and Toyota's could be as much as $800. If you are 100% certain it is the CAT then save the $$$ and go with aftermarket.

Like the person said... bank 1 could be before the CAT. When I had that code it was my o2 sensor after the cat??? (but I think it said bank 2... but not positive... happened 4years ago)

My advice is to replace both o2 sensors, it's only a little bit of time before the other will go unless you are possitive that you need to change only the one before the CAT. (Usually the one after the CAT fails first)

Get DENSO o2 sensors... that is what came with your car. The cheapest place to buy it is at Amazon. Get a direct fit model for both. Google Denso O2 sensors to find out the part number... then go to Amazon.

Go to a corner garage (not a chain) and hope thy charge you between $50 - $100 to install them.

[EL CONTRADOR]

Hi!!

I've been reading A LOT on this P0420 problem and found out a few good thing you might like to know!!!

I lot of people have the same problem that we do, some changed everything related to emission system. Cats, o2 sensors, MAF, MAP, Temperature Sensor and still had the light coming on!!

On thing that not a lot a people think of checking is the Ethanol rating in the gasoline they use!! Toyota tacoma are set to use Gas with less then 10% ethanol... So what i did is I empty my tank and filled it back with ethanol Free Gasoline, unplug the battery to erase the codes and Guess what, no more light...

The problem with ethanol is that it doesn't burn like regular gas at all and our O2 sensors do not reconised the exhaust gas so your check engine light turn on!!!

I was using Gasoline that had 12% Ethanol and didn't know it!!

Try that and let me know what happens

Thanks