Wacky O2 Sensor

[IndyBob]

I have a 2001 Pathfinder with about 110,000 miles and received a P0140 code that an O2 sensor wouldn't talk to the computer anymore, so I bought a new OEM (Bosch) O2 sensor at AutoZone and replaced the sensor -- Bank 1, Sensor 2. I had Nissan replace an O2 sensor about 15,000 miles ago. Then I used a diagnostics tool to reset the codes.

After this I was great for 75 miles, but the Service Engine Soon light came on again. This time the code is P0138 - Circuit High Volts (same bank, same sensor).

What do I do now? I kind of doubt the sensor went bad that fast. Any ideas?

Thanks,

Bob

[IndyBob]

P.S. Nissan reprogrammed the computer when the first O2 sensor was replaced.

[nissandoms47]

you should have bought an oem nissan 02 sensor. not an autozone one. they're totally different. i had this problem. i had to go buy nissan sensors and havent had a problem ever since.

[IndyBob]

Thanks, but they sure looked identical right down to the different colors on the different clips where the cable mounts. Also, when Nissan replaced my first O2 sensor, they used Bosch and said it was OEM.

[fueler]

Bosch parts are made in Germany, while Nissan uses NGK O2 sensors which are made in Japan. In my experience, whenever I have used a German part on a Japanese car, it ALWAYS causes problems. Spark plugs, O2 sensors, whatever it may be, keep it Japanese. A great rule of thumb is Keep german with german, keep japs with the japs. German components are about as good as their vehicle electronics (I.E. - they suck)

[nissandoms47]

yes it may say bosch on the replacement from nissan, because they are bosch, but the actual compound inside of the sensor is different. even though it says bosch its different. thats why you never go to autozone for things like 02 sensors. oh and nissan doesnt use NGK 02 sensors. they use NGK plugs.. well at least my 96 r50 and my 97 jr50 and my friends 98 r50 came with stock bosch ones.

oh and has your exhaust been replaced or taken apart or anything lately?

[IndyBob]

My bad, I got the sensor at Advance Auto Parts, not Auto Zone. Either way, it did look just like the one I took out and it did say "Made in Japan" on the package. I haven't had any work done to the exhaust system, ever, other than the O2 sensors.

At this point I reset the sensor again, added some injector cleaner, filled up with premium, and cross my fingers.

Thanks,

Bob

[nissandoms47]

humm im still sticking with go buy the nissan one. the element inside is different then the one you have. I asked about the exhaust system because when i took my engine out, i reused the old gaskets, oxygen would leak into the system right before the 2nd o2 sensor and trip a code because it thought the engine was running lean..

[KoukiS14]

man. . the Bosch 02 sensors were always the way to go with the 240s.

[jcogley]

I'm having the exact same problem on my 99' q45, (same codes..everything). I replaced the O2 sensor with an OEM and got the 138 code after about a week. Tried gas additive to clean injector...no luck...came on today again.

Other threads mentioned ECU replacement , a bad injector dumping fuel and even a short in the engine harness at the plug to the O2 Sensor.

Do you feel a miss/misfire?

I'm putting mine in the shop next week to troubleshoot. I'll let you know the outcome.

Keep me informed too.

Aggravating and expensive.

[IndyBob]

When I was first getting the "bad O2 sensor" reading, I did always feel a single misfire in the engine. It was always in the 45-70 mph range, and always when holding a steady speed or ever so slightly decelerating. The 138 code came shortly after replacing the O2 sensor.

For all the research I tried, no one could explain what a 138 code means you should do, other than to replace the sensor, which I had just done. My local Nissan shop confirmed that they use Bosch, and, frankly, the sensors, cables, clips, etc. were completely identical, so I doubt it is an "Advance Auto Parts sells junk" sort of thing.

Since the car seems to run OK, I went ahead and reset the ECU. I also filled the tank with premium gas, and added the fuel injector cleaner (whatever Costco sells). Since my 138 code came 70 miles after changing the O2 sensor, I figured that I may not see anything for a while, if ever. I have now run about 250 miles, run through the tank of gas, added regular unleaded, because I am cheap, added another thing of fuel injector cleaner (Costco sells a 4-pack), and, so far, no codes have shown up.

Maybe I'll luck out. All I can say is that if the car seems to be running OK, try resetting the ECU a couple of times. Since the 138 code basically means that the fuel is either too rich or too lean, it shouldn't cause you any problems, like the engine blowing up, just maybe some extra emissions and/or worse gas mileage.

Regarding other threads, I doubt it is the ECU or other codes would be showing up as well. A short can always cause problems, but the cable cover seems pretty tough, and, if you hit all of the clamping locations (yeah, one of them is a real pain), then I don't see how it could be this. Don't know about a bad injector -- I have never had one go bad. I would think that you would notice a lot of misfiring and/or loss of power though.

Good luck (for both of us),

Bob