mb12345

The CEL in my '97 ES300 (112K miles) is on and the code is P0135. I read all the previous posts here about this being for O2 bank 1 sensor 1, which is located between the engine and the firewall. I am sorry, I do not understand much about cars so have to ask a couple of dumb questions. What exactly is the firewall? To replace the bank 1 sensor 1 O2 sensor, does the technician replace it by popping the hood, or does he go underneath the car and replace it?

When I take it to my mechanic, I just want to be sure he is replacing the right one.

Thank you.

JSM1284

The firewall is the metal wall between the engine and the passenger compartment.

mb12345

Thansk JSM1284. Do you know whether the sensor 1 bank 1 is replaced by opening the hood or by lifting the car and going underneath?

charley240

iTrader: (6)

if its the one you say it is, lift the hood. it should be right in front on the exhaust manifold. its in plain view pretty much. if youre not comfortable doing it, i would suggest paying someone to do it. you dont want to ruin other things.

goodluck
Charley

mb12345

I will be taking it to a mechanic to do it. I wanted to know where this sensor (bank 1 sensor 1 - p0135 code) is located, just so that when the mechanic replaces it, I would know whether he replaced the right one. In some other posts related to P0135 CEL code, I read that this sensor is in between the engine and the firewall for the es300. Is that not correct?

csaxon

mb12345

Thanks for the pic

mb12345

Upon reading several other threads related to P0135, I see some people who replaced bank 1 sensor 1 had their CEL come back on. It was suggested that the "other" O2 sensor be also replaced. Is this other sensor referring to bank 2 sensor 1 or the bank 1 sensor 2?

Lexmex

This can indeed happen. That other sensor that would be replaced would be bank 2 sensor 1. Bank 1 sensor 2 is the sensor that is found after the catalytic converter underneath the vehicle and is actually a different type of sensor than the two sensors found off of each of the engine banks.

mb12345

Since I have to replace bank 1 sensor 1, would you suggest I also replace bank 2 sensor 1 at the same time? Or replace the first sensor and see if CEL comes back on, and then replace the other sensor if needed?

Lexmex

I would wait to see if the CEL comes back on and then take readings of the banks to see what the ranges are and report them here.

mb12345

Ok, so I replaced the bank 1 sensor 1 i.e. the sensor behind the engine near the firewall. 2 days later, I got the CEL back. I took it to autozone and they say it is P0420 (catalyst efficiency below threshold).

I had the p0420 about 6 months ago. At that time I had replaced the catalytic converter. I did not get the CEL for P0420 after that.

Any ideas why I got the P0420 now, after I replaced the O2 sensor near the firewall?

Lexmex

You're right, usually the P0420 is the cat or the O2 sensor. I know of some other possibilities, but the first two are the main ones, so I'll list them and give you the rest of the possibilities:

1. The cat- since you replaced it, it should be okay, but a gas analysis test (basically an exhaust shop might have one of these can check the HC, NOX and CO readings and see what's up)
2. O2 sensor- only thing I can say here is to make sure you use an OEM part, not something aftermarket. These vehicles are particularly picky about sensors. I know of some guys on www.solaraguy.com that have run O2 eliminators to knock out such issues.
3. Weather- it was quite common to see P0420 in Mexico with vehicles, because high altitude means less oxygen. In addition, if you have hotter weather, that can affect the combustion cycle and resultingly increase emissions levels.
4. Bad compression- Ah, this one might not be apparent. If you have issues with your compression, a.k.a., blow by in this case, oil can seep into the combustion cycle and can affect not only the precats but can seep through to the main cat. Overfilling the oil can do this, but the main time I see this is when there are compression issues. Also, if the oil is old, that can also do it.

Keep in mind, the O2 sensor after the cat doesn't read the 3 main components of basic emissions tests, it looks at the wavelength coming off the cat.

JSM1284 may also have some fine input on this, I have high respect for his insight and experience.

mb12345

Lexmex - Thanks for your response. The sensor I replaced for bank1 sensor1 was an OEM sensor purchased from a toyota dealer.

So you are saying I should do a gas analysis test to ensure the cat is good?

Should I also replace the bank2 sensor1 (near the radiator) or the bank1 sensor2 (post cat)?

I hope JSM1284 can also provide his input here. For JSM1284, the summary of the problem is, I had P0135 so I replaced bank1 sensor1 with a oem sensor. Now I get a CEL again with P0420. I had replaced my cat about 6 months ago when I had P0420, so I am at a loss why I got P0420 again after replacing the O2 sensor.

Thank you.

Lexmex

Well, if all you are getting is P0420, you don't want to change the A/F sensor unless you are getting an A/F sensor code. P0420 is tied to the cat, O2 sensor after the cat, or some temporary condition (even bad gas and/or conditions that I mentioned.). You can try resetting it with an OBD2 reader or just pull the battery cables for a bit.

The gas analysis test would at least show if your readings are in order. Usually I find with newer vehicles having such an issue to have their HC (hydrocarbons/unburnt gas) to be a bit high. Often this could be a sign that spark plugs need changing, but it's rare. Older vehicles generally run into NOX problems, that are more endemic to needing the cat converter changed out.

I am not suggesting this, but when I had a few A/F sensor issues in Mexico, I would often run either Techron concentrate or a bottle of Redline's Fuel System Cleaner (Pep Boys is where I have seen this) to help clear out the system. You can actually hear popping from the catalytic converter after this and I found it can help clean out some deposits (the Techron was particularly known for cleaning out sulfur deposits, of which Mexican gas was loaded with).