I finally found the money to replace the O2 Sensor in my 97' Blazer, 4X4 2 Dr.

What do I need to know before replacing it? I know there are multiple O2 sensors, and the last thing I want to do is to replace the wrong one. (Its been done before.) The one I know I have to replace is before the Cat., and I know there are two before that, usually numbered, which are which? I believe it is sensor 2 that has gone bad, but am going to double check as I have access to a new Snap On Solous Scanner, best be safe. Could someone please help me, and point out the locations of sensor 1 and 2 please?

 

On a '97, you should have 4 sensors total. B1S1 (bank 1 sensor 1) is on the driver side down pipe a few inches down from the connection between the driver side exhaust manifold and the y-pipe. B2S1 is located on the passenger side down pipe, just a few inches forward of where the driver and passenger down pipes come together to form the 'Y' of the y-pipe. B1S2 is the pre cat sensor and will be the sensor directly ahead of the catalytic converter. B1S3 is the post cat sensor and will be located just behind the catalytic converter.

With B1S2 & B1S3, I would recommend swapping the pre-cat and post-cat sensors and watching to see if the code follows the sensor. These two sensors have nothing to do with the operation of the engine. They are catalyst monitoring sensors only.

 

I replaced what was thought to be the faulty sensor, with a Junkyard sensor a month or two ago. But we had to take a guess which sensor was which at the time. Code was for B1S2. But went I scanned it before hand, today I got Cat. Efficency Low, not the one reguarding the O2 Sensor. I replaced B1S2, anyways with a new Bosch, O2 sensor. (I don't like having junk in my truck, and now I know which is which) Went to clear codes, again, hopefully it will go away. That O2 sensor that was in there wasn't in great condition at all, but would it cause that kind of code "Cat. Efficency Low", and if I need to replace my Cat., how big a job is that, and how much can I expect to pay Part wise? (I know people so free labor.) Also what kind of Diagnosing should I do, you mentioned that these are monitoring sensors, so more than likely my problem may lie here or perhaps my O2 sensors are functioning correctly now, and are now telling me something is wrong with my cat?

 

It is always possible that something is wrong with the catalytic converter. Again, what is the specific code that you are getting (Pxxxx)? With this code, I can look up the specific diagnostic.

As far as part costs, well, new high flow universal cats can be purchased for under $100. This would be for a weld in unit. The bolt in units are more expensive.

 

I just got it scanned again, and the code didn't come back, im not too worried about it.