P0420 and P0133 codes
 

Well I am throwing both of these codes relating to the cat/02 bank 1 which I am assuming is referring to the cat/02 right off the manifold? Since it is a 98 2.3L AT and there is only one exhaust bank. Any corrections and/or known fixes from any of you on this would be well appreciated. I saw the vid on detecting a bad cat and am going to try to maybe check that out with a temp gun. But didn't know if any of you had ever had this specific combo and what the fix ended up being. Thanks!

These are the Possible causes for p0420

- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM)

But since it is also throwing the p0133 which possible causes include
- Faulty Front Heated Oxygen Sensor Bank 1
- Front Heated Oxygen Sensor Bank 1 harness is open or shorted
- Front Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Inappropriate fuel pressure
- Faulty fuel injectors
- Intake air leaks may be faulty
- Exhaust gas leaks

I would say its a good bet that you have a faulty O2 sensor or an issue with the wiring for the O2 sensor.

Its possible that the cat is failing as well as the O2 but most likely its just the O2

Example is mine threw the p0420 code at the same time as the insufficient egr code and (which i knew my egr passages were clogged already) when i cleaned the egr passages the p0420 code went away as well and has not returned since. Alot of times that code will tie into another code when thrown together.

Also wanted to say that before you go and spend 70 dollars on a new O2 sensor, get under the car and do some testing/checking because even though the O2 is "probably" the issue it could be the wiring to that sensor, it could be that your exhaust tubing has a significant leak somewhere like the doughnut gasket between the sensor and the cat, and could also be a faulty fuel injector (however unlikely)

On a 98 the front O2 sensor isn't "under" the car. It's right up front on the exhaust manifold.

Per jimblake's info that is where you'll wanna start your testing/checking.

Thanks jim, i forgot they moved it forward on the 98's

Cool...thanks...I will check that out. Considered just putting a header on it at one time but we'll see. Don;t really care to do that but if its cheaper than a cat replacement in the future why not...? Could just do that and an 02 for $150.

Well, that depends on whether the cat is in fact messed up. If it IS, then a header & a new O2 sensor won't fix it.

Agreed, like jim said, start by testing and checking and try and narrow it down to the actual issue and then if you have it narrowed down to the O2 and not the cat then look into a header and new O2.

On a side note; If the idea behind a new header is "power" know that other than the sound your not really gonna see a noticable increase in HP or torque.

Yeah, power was not on the top of the list as this is just my little gas baby.....but if it would help with mpg too, I might consider it more. I know that can go either way, but I wouldn't necessarily drive it differently.
As far as a faulty 02, I have heard different views that are valid points. Some mechanics say that if an 02 is throwing a code it is more than likely that another issue is at hand (ie injector, cat, etc.) And the 02 is just simply doing it's job. How do you guys feel about that? On the other hand, at 89k miles, is it a common thing for an 02 to tank and start throwing codes. If so, then maybe replace that.....
I do run Amsoil, as I am a Dealer, and the higher levels of Zinc tend to clog cats long term so that is a good possibility. This car has ran on it for 3 years or more I would say. But the pros outweigh the cons in my opinion so replacing a cat is no big deal if need be. Is there a way to test out an 02 being faulty rather than just replacing it?

Faulty catalyst is measured by the REAR O2 sensor. Even by 1998 they were fairly good at telling the difference between a bad cat vs. a bad rear O2 sensor.

But yours is throwing a code for the front O2 sensor. IF(?) the front O2 sensor is causing the mixture to go too rich or too lean, that might be influencing what the rear O2 sensor sees. It's a cause & effect that almost makes sense, but you can't really bank on that. However, it's reasonable to chase down the problem with the front O2 sensor first, then just wait & see what happens with the P0420.