O2 and Catalytic converter question

[Rexsname]

I want to know how it works, but I have no knowledge of chemistry and very little of electricity....................

My '01 Tacoma has 191,000 odd miles and the check engine light (CEL) lights up about once every six weeks or so. Usually just after a extended coast or when just putting around off road (not on the gas).

The O2 sensor was replaced about a year ago.

Today I found out that replacement 'cats' would run almost $1900!!!! I can live with re-setting the CEL every so often but what exactly does this combination of emissions equipment DO? Am I likely to see an increase in MPG?

I also am due to replace the timing belt sometime very soon and our financial situation is still not the best. Which job should be done first?

REX

 

[madizell]

You can't make any assumptions about what might be causing the CEL to light, as there are a number of things that can do it, all emissions based, but many having nothing to do with cats or O2 sensors. You will need to get the trouble codes out of the computer, and if that is not something you can do, have it checked by a technician. It could be anything. A good scan tool can cost upwards of $200 (or a lot more if you want to go top of the line) or just pay someone else to do the work. These days, guessing about engine problems is not a good use of time.

 

[toy_tek]

Agreed.

Keep in mind Checker or Autozone will read your CEL code for free, it only takes a minute.

Once you find out what it is post it up.

 

[Rexsname]

P0420 Catalytic System efficiency below threshold Bank 1


I have access to a OBDII scaner at work, and the code is the same each time.


REX

 

[RoundOut]

P0420 Catalytic System efficiency below threshold Bank 1


I have access to a OBDII scaner at work, and the code is the same each time.


REX

Whatever you do, don't let the shop you choose to do a catalytic swap screw you on your core. I have a "buddy" who makes about $300 on EACH core, selling them to a scrap guy. The catalyst contains platinum, aparantly in enough quantity to make them that valuable. I quote "buddy" because although he takes care of me, I don't trust him as far as I could throw him. :ar15:

I don't know if you can sell them individually, because there have been a rash of recent cut-off crimes in the mall parking lot, particularly targeting LCs. It sucks, but it only takes a theif a couple minutes to pull up next to your SUV, saw off the TWO cats, and bug out. You won't notice until you turn your engine on and no longer have any mufflering. There may be limited market, as the markets may be suspect of individual units.

.

 

[Rexsname]

Yeah I am counting on recouping some of the costs involved with my 'cores'. I've seen E-bay cats ("new OEM") for $130 and the dealer wants almost $1900. I cant afford to get a new truck, dont want to.


REX

 

[toy_tek]

If I understand correctly, the 420 code merely monitors the cat efficiency. It does nothing for engine performance or engine efficiency. There is a "fix" where you can basically make a box with a diode (or something like that) that you plug into the connector instead of the 2nd O2 sensor that gives the ECU a constant voltage value and keeps the CEL off. I can probably dig up more info if you'd rather not replace the cat right now.

 

[Rexsname]

What does the catalytic converter actually DO? I feel a bit apprehensive about bypassing a well engineered system by 'fooling' the computer into doing something it wouldn't normally do.

Just by its name I'd assume (yeah, I know) that it causes a change [catalyst] and then converts it into somethig else. Use small words, please, I never took chemistry.......

Can anyone explain why I should not go with one of the E-bay "cats" and not spend almost six times the cost for converters from either my local dealer or this forums' sponser. I plan on keeping this truck for quite some time, a replacement is NOT in my plans.

REX

 

[toy_tek]

As I routinely do when I'm faced with a question and not a comprehensive answer, I wiki: http://en.wikipedia.org/wiki/Catalytic_converter

In a nutshell, the cat burns off extra-toxic particles from the engine combustion process. Leaving your exhaust squeaky clean and odor free. Ok well maybe not exactly.

By bypassing, you are merely cheating the ECU as well as the environment. How this sits with your morals, well only you can answer. It is illegal. But I read about it on the internet so I feel compelled to spread the word.

 

[Rexsname]

I thought that I was told that the O2 sensor told the computer how to adjust the air/fuel mixture for the best efficiancy. Wouldn't eliminating an agent of change allow/encourage bad data into the computer?


Do catalytic converters typically "clog" or come apart over time? Is this a consumable item like brake pads? Or will they last like a block, crank or cam, a long, long time with proper maintainence?


REX

 

[toy_tek]

Yes the primary Bank 1 sensor 1 O2 sensor is what triggers the air/fuel ratio to the engine. The Bank 1 sensor 2 O2 sensor is what tests the cat efficiency. Sensor 2 does not impact the air/fuel mixture.

from the link I posted above:

In vehicles with OBD-II, a second oxygen sensor is fitted after the catalytic converter to monitor the O2 levels. The on-board computer makes comparisons between the readings of the two sensors. If both sensors give the same output, the catalytic converter is non-functioning, and must be replaced. It will also spot less serious damage to a catalytic converter, such as the use of leaded racing fuel in an on-road vehicle.​

I've heard cat's can clog. This would be due to an improperly running engine, or maybe an oil or fuel additive that shouldn't be there. They can also corrode from the inside - essentially the grid will crumble apart and you can see right through it (from the inlet/outlet) with no obstruction. In my experience as long as your engine is running correctly, you shouldn't have any cat related problems. Corrosion might be another issue. I saw a lot more corrosion related cat issues when I lived in the rust belt of Northern Ohio.

As far as aftermarket - I don't know of any pros or cons regarding them. We sold them all the time 15 years ago when I worked at an auto parts store, never any issues that I heard of. For the price difference I wouldn't hesitate to install one.

 

[Rexsname]

Thank you for the Wikipedia link, even tho I didn't understand the chemistry part.


I guess the OEM parts are expesive for a reason, I just can't quite grasp the magnitude of difference in price between "New OEM" E-bay price and the TRDParts4U price.

REX

 

[JJackson]

Rex I was just reading over on AZTTORA about stolen cats and the options for replacement, might want to check there as well. Take the truck to PHX and see if someone will steal them so you can get new ones.

 

[Rexsname]

Yet another reason NOT to go to PHX

REX

 

[RAV4fun]

I have the exact same code on my RAV4 right now. I've ordered a new downstream O2 sensor (the one after the catalytic converter) on the advice of several Toyota mechanics I know. I'll be replacing it next week and can let you know if that takes care of the error and CEL...

The O2 sensor ran me $89, and I'm told the replacement will take a non-mechanic like me 10 minutes, so even if it's not the cause, it's not too steep for a first attempt.

The reason I'm going with the O2 sensor first is simple, the error is saying that the efficiency is not correct...and the downstream sensor is the one that monitors that efficiency...so replacing that sensor SHOULD transmit the data to the ecu...and clear the code...someone with some actual knowledge in this area, feel free to correct me...