DTC P0138 – How to Service Your 02 Sensors

DTC P0138 – How to Service Your 02 Sensors


The OBDII Trouble Code DTC P0138 refers to your secondary oxygen sensors, and is triggered when the sensors provide too high of a value to the ECU. When the PCM sees more than 900 millvolts bring sent from the secondary 02, the P0138 trouble code will turn on.

Other OBDII trouble codes that can accompany this issue are P0132, P0158 in relation to your secondary 02 sensors. We’ll be testing this trouble code and showing you How to Service Your 02 Sensors in a 2006 Infiniti G35. This Nissan check engine light can mean that your catalytic converter may have failed.


Symptoms : Typical symptoms of this Check Engine Light will of course result in the check engine light illuminating, but your vehicle may idle and drive rough as well. Your vehicle may enter limp mode depending on how badly your fuel economy has decreased. 

Things you need to do : Locate and discover which 02 sensor you are having a problem with. Your secondary 02 sensors are part of the Y pipe that sit in the middle of your vehicle and connect your headers to your axleback exhaust.


This check engine trouble code can arise when your secondary oxygen sensor has failed or there’s a short in the wiring from the sensor your ECU. You may also have a ECU error or excessively high fuel pressure for some reason. However if your car still drives and does not enter limp mode, chances are it’s the secondary 02 sensors.

If this vehicle is meant for “off-road” use only, you can just resolve this issue with an 02 sensor simulator. Keep in mind however that this will more than likely break any laws of your state if you drive it on any public road. Please be responsible.

How To Install a Check Engine Light Eliminator

To determine which 02 sensor you are having a problem with, we’ve provided a color code as well as this image which should show you which one to replace. This step is crucial if you want to learn how to service your 02 sensors.



Bank 2 and Bank 1 are also conveniently color coded so that you can’t get mixed up even when the 02 sensors are unplugged.



The secondary Bank 2 oxygen sensor connector is green, while the secondary Bank 1 oxygen sensor is blue. Once you have tracked down the connectors, test the continuity to your PCM or ECU to ensure it’s not a wiring issue. Continuity should exist through these wires, so grab your voltmeter and get to work.


The Bank 1 Secondary 02 sensor is a four wire 02 sensor, and the terminals are printed on the inside of the 02 connector, identifying the pin you need to test. The same applies to the Bank 2 secondary 02 sensor, so let’s take a look at the 02 sensor pinout.

  • Bank 1 sensor
  • 02 wire 1 – ECU terminal 16 – 02 wire 2 – ECU terminal 75 – 02 wire 5 – ECU Terminal 35 – 02 wire 6 – ECU Terminal 56
  • Bank 2 sensor
  • 02 wire 1 – ECU terminal 76 – 02 wire 2 – ECU terminal 77 – 02 wire 5 – ECU Terminal 57 – 02 wire 6 – ECU Terminal 58

Make sure to test this with the vehicle turned off, and your ECM and wiring unplugged. Continuity should exist here, if it doesn’t that’s the culprit. Try running a temporary wire to the ECU terminal and see if that improves the situation. If continuity does exist, let’s move onto the removal part of our how to service your 02 sensors article.






Reconnect the ECU and start your vehicle, now you are ready to test your secondary 02 sensors for failure. You are  testing the sensor wire and the ECU pinouts shown above. Pin 74 for the Bank 1 Secondary 02 sensor and pin 55 for the Bank 2 sensor. Start your car and rev the engine to 4000 rpm and hold it there while testing the values to the ECM.

Once you have determined which one of your 02 sensors has gone out on you, go ahead and replace them using these part numbers. Bank 1 is part number 226A0-AM601 and the Bank 2 sensor is 226A1-AM602. Replacing these secondary 02 sensors is a very easy and straightforward step in our how to service your 02 sensor guide.

Be careful not to damage the threads on your secondary 02 sensor, as this bung is located inside your actual cat. Damage to these threads will be extremely costly, or you may have to resort to extreme measures to repair.

Don’t let this happen to you

You have now completed our How to Service your 02 Sensors guide and resolved your P0138, P0132, P0158, or P0420 OBDII trouble code. Have any questions about your OBDII check engine light? or about our how to service your 02 sensors guide? Leave us a message below and let us know.