Love this site! Just bought a 99 Max and need to replace and O2 sensor. Autozone coded P0138 and says it is Oxygen Sensor #2. Where are the 3 sensors located, not sure which one to buy. Any help would be great. thanks

 

I'm not sure why they would call it sensor #2 but it is the one in the cat. There is one in each leg of the Y-pipe and one in the catalytic converter. In the Haynes manual it says "Downstream oxygen sensor maximum voltage monitor fault". Who knows what that really means but if you had a CEL I would clear the ECU and check it again in a week or so or wait to get a CEL again. Sometimes sensors will throw codes for no logical reason...

 

My 99 SE has the same exact problem. It is the bank 1, sensor 2 (0138), which I believe is the driverside behind the cat. What kind of problem is your sensor throwing. The reading on my sensor says that there is no reading from that sensor, and that there is high voltage coming from it.

 

I have a 99 gle and my sensor went out. I went to Ancira Nissan (San Antonio) and paid 171.00 to replace it (including the diagnostic test fee). Then I saw the other thread about how to get the engin codes from below the gas pedal and I feel like an idiot, oh well, such is life. My bad sensor was the rear sensor, which according to Nissan is the cheapest one to replace.

 

Thanks for the reply! The print out they gave me at Autozone reads, input voltage is to high for current operating condition. I'm confused as well. Do you think our sensors are bad or could be another problem? Wish the readings would be more specific, like if they were to say, FIX the O2 sensor on the Cat, its broken! Wouldn't that be nice. Has your car's MPG changed or is it driving rough?

 

When I had the code pulled, Autozone turned to CEL off and it came back on within an hour or so. Did they clear the ECU, or do I have to do it a certain way, Would taking to ground wire off the battery clear the ECU?

 

Got some good info off the search feature. Since you have the same thing going on with your car, I want to pass this on. Just purchased Bank 1, sensor 2 for 58.00 + shipping From Brown Nissan in Tempe. Ph(800) 810-8123 ask for wholesale parts. My local dealer wanted 103.00 for the part. Courtesy wanted 68.00 + shipping. I hear it is a cinch to put in. Thanks again for your input.