For a 96 Blazer 4x4:

So I've got my CT emissions test coming and I've got a couple issues.

First my check engine light is completely out, so I'll have to get a new bulb installed, but that isn't really my problem right now.

My friend has one of those OBD II code readers and he scanned my truck to see if I had any CEL's since the bulb is out in my dash. I only got one code - P0141 - 02 Sensor heater circuit malfunction (Bank 1, Sensor 2). This is my only CEL.

I've had this truck for about a couple years now and supposedly the guy I bought the truck from (a friend of mine) had the cat hollowed out. Not sure why he did that, but that's what he says was done.

Obviously, to pass emission, i'm going to need a working cat. My question is, would a hollowed out cat throw this code? Would a hollowed out cat throw any other codes because this is the only code that I'm getting.

 

That is a code for the pre-cat sensor which is just in front of the catalytic converter, specifically the heater circuit in that sensor so it doesn't have anything to do with the catalytic converter itself. The truck should throw a catalyst efficiency code if the cat were not functioning properly and nothing was done to 'trick' the B1S3 sensor.

You can use the diagnostic steps provided in the link below for any of the O2 sensors. The wiring references will be different though:
P0135 - HO2S Heater Circuit Bank 1 Sensor 1

 

Maybe the cat was never hollowed out then. I don't know if it was or wasn't since I wasn't the one who did it, but if it's not throwing a code...?

Doing a little research, doesn't Bank 1 sensor 2 (P0141) monitor the catalytic converter? If the sensor is no good, how is it supposed to know if the cat is working or not? So, once the sensor is fixed and working, is it going to throw a code for the cat if the cat is no good?

 

Bank 1 Sensor 2 heater circuit malfunction means the heater on the o2 sensor itself is malfunctioning (most likely cause). Replace the sensor. The other causes include cut wires, split wires, corrosion, etc.

Yes Bank 1 sensor 2 monitors catalytic efficiency, however, the heater circuit is not working, meaning the heater inside the sensor is malfunctioning. The o2 sensors will heat up on their own.

Replace the sensor, clear the code, and continue driving your truck. If the code comes back, then the problem is in the wiring. If the code does not come back then the sensor was at fault. If your cat was hollowed, after you replace the sensor, the o2 will be monitored again and look for cat problems. If the cat is bad, after replacing the sensor, a catalytic efficiency code should pop up.

 

Ok, thanks CSC, I get what you're saying.

So let me ask you this, what if the problem is BOTH, the heater circuit AND the catalytic converter... would that throw two different codes then? Right now, I'm only getting that one P0141 code and that's it.

Also, what does this sensor cost? I was looking at parts websites and saw them ranging anywhere from $50 to about $140. I think the Bosch sensors were the most expensive. Does it really make a difference which sensor because that's a pretty big price difference?

Also, is there an easy way to tell if the cat was hollowed or not without waiting for the code to come up or without taking the cat off? I've got to get this emissions passed in about a month or I can't get it registered, so I really don't have much time and want to get everything done.

 

Okay, First question:
If the heater circuit is malfunctioning, usually the PCM will not register another code with the sensor. It sees it's not functioning properly, so it basically ignores it and goes into closed loop operation. So, theoretically, you will only have the one code, and which ever code is more important will be the code that is stored in the PCM. A cat code is an important cdoe since it's emissions related, but like you said earlier, if the o2 isn't working properly the PCM can not rely on it's signal. So, by that statement, yes, your cat can still be bad, however, it will be unknown until the sensor is working properly again.

Second Question:
GM and Bosch don't get along very well. I'd have to recommend to put in an AC Delco part, but if your short on cash, whatever you can afford will work to get passed emissions.

Third Question: (This only applies if your truck is NOT currently registered. If it is registered then after replacing the sensor, continue to drive as you normally would)
This is what I'd do if I were you. You can get the thing registered until it's already been inspected, correct? If thats the case, then DO NOT CLEAR THE CODE. Let the PCM clear the code for itself. This is done by replacing O2 sensor, then running the truck for awhile. If you have a large yard, or a good field, go run it in the field for a bit. It should shut off fairly quickly. If you don't have a field to run it in, then if you feel comfortable, take it up and down your street once or twice. (Only do this is you feel comfortable! I am not advocating driving without registration) Just enough to get to about 40 mph, maybe 35 mph, then back down. That should clear the code.
Now I say don't clear the code with a scanner because if you have the ODB II scan test inspection then you may clear out all of the sensor data, which will result in a failure of the emission tests.
If you DO NOT have the OBD II plug in test, and just the sniffer test, then go ahead and clear the codes with a scanner. You will still have to run the truck for a short amount of time to find out if the Cat is working. Don't be surprised if you have to run it today, then go out again tomorrow and run it again before the code comes up.

I hope I've answered all your questions. If you have any more, lemme know.

 

Thanks for the advice... good stuff.

The car is registered, but can't get it re-registered without passing emissions. That's what I need done. Registration needs to be renewed in a month or less, so I'm able to drive on the street for the next month.

So for now, I'll just replace the sensor and I won't clear the code. Hopefully the code clears and I don't have to replace the cat too. If it doesn't clear in a couple days after replacing the sensor, I'll have it rescanned and see what codes its still throwing.

I'm in connecticut and we do have the OBD II plug in test. They will not pass us if the computer is not "ready" or has been cleared recently. If the check engine light is on for any reason, the car fails right there on the spot.

 

that would suck if the check engine light came on right when you get to inspections. but anyway it could also be that something just acted up in the computer to throw that code.

 

The B1S1 & B2S1 sensors are solely responsible for fuel management in the engine and are the only two sensors that have anything to do with open or closed loop operation. B1S2 is used as a pre-cat monitor and used as a comparison with the B1S3 sensor for monitoring the catalytic converter. The B1S2 & B1S3 sensors have no feedback to engine operation.

The heater on the downstream sensors only decreases the time it takes for the sensor to come up to temperature. As I said earlier, the heater circuit has no effect on the catalytic converter itself and the sensor will read properly once it comes up to temperature so if you had a hollowed out cat, you should have a code for catalyst efficiency.

Replacement of the sensor may fix the problem, but I am a firm believer of diagnosing a problem rather than just throwing parts at it. Throwing parts is a surefire way to spend money and increase frustration if it doesn't work out in your favor.

As a DIY diagnostic step, you could swap the pre-cat (B1S2) and post-cat (B1S3) sensors and see if the code changes to P0147 for the B1S3 Heater Circuit. If it does, replace the sensor (now in the B1S3 location) and be on your way. If P0141 comes back, then the sensor wasn't the issue and the wiring should be checked next.

 

So, if I try out your test, how long after I switch the sensors on B1S2 and B1S3 does it take to throw a new code - if it even does throw a new code? Would this be on the next start up or I'll have to cycle the pcu once over?

Man this 02 sensor is not budging. Tried the wd40, warming up the car, and i have the 02 socket and it's not budging at all. What a pain in the *** this is.

Any tips to get this rusted piece off that i havent tried yet?