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2001 Nissan Sentra Question: Constant P0140 O2 sensor code

 

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jmansf3, 1.8L 4 Cylinder, Fords, NJ, March 24, 2013, 18:50
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I have a 2001 Nissan Sentra that keeps showing a P0140 DTC. I was intitially getting a code for the heater circuit so I replaced the sensor. Thats when I started getting P0140 instead. I checked wiring for shorts and continuity to the ECM as stated in the factory service manual. Everything checked out good so I replaced the sensor again and have the same results. The code states bank 1 however the factory service manual states bank 2. in the end I ended up replacing all 4 sensors since one by one I was getting codes. All DCT's cleared up after replacing except this P0140 which keeps coming up. On the scan tool the sensor reads a constant 1.275 volts. I have checked with 2 different scan tools with the same results. I also checked all grounds and cleaned and tightened them as well. I don't know what else to try.

Thanks
John

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    pushrod March 25, 2013, 04:24
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     Master

    Defective aftermarket sensor, post cat! NGK/NTK, DENSO brand work well. Circuit fault to/from sensor can be checked with DVOM.

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  • Answer #2

    Greg's Orange Auto (12933 Answers) , Orange, CA - (714) 361-9386
    globalhelper March 25, 2013, 06:27
     Master

    where are u buying sensor? iv seen aftermarket sensors cause a number of issues incl car runnabilty issues

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    jmansf3, March 25, 2013, 08:58
     Rookie

    Purchased from pep boys. I bought Bosche sensors since they were the same brand that came in the car. Also made sure they had factory plugs already. I checked circuit with DVM and all looks good. Everything pointed to bad sensor so I replaced it a second time with same results.

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    pushrod, March 25, 2013, 09:15
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    5 volts reference and ground at the 4 wire plug key on? 12 volts and ground for the heater cifcuit also at the 4 wire plug? Another way to check the 12 v heater citcuit is turn key on with sensor pluged in should get hot holding in hand! The sensor BEHIND the converter! Any blown fuses? Check ALL!

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    jmansf3, March 28, 2013, 20:10
     Rookie

    OK, I had a chance to check out your suggestions. I have confirmed 12 volts and ground. I verified heater current however there is no 5 volts reference. I checked other downstream o2 sensor which is working normal and got the same identical readings on both plugs. I did notice for some reason my bank 1 fuel trims especially short term fuel trim was high around 20%.Bank 1 upstream also seems to stay more around the .05 volt readings but does fluctuate between 0 and approx .8 volts while operating the throttle and seems to function normally while driving. Also I noticed the ECT on scantool does not rise above 170 degrees while driving. I should also mention I checked for reference voltage with key on engine off. Not sure if that is the correct way. No blown fuses either. This is so frustrating. The car runs very good but can't get through emissions. It does idle maybe just a little rough after it warms up and idles relativly rough when ac compressor kicks on.

    THANKS FOR ALL THE RESPONSES SO FAR!!!

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