TEST 2: Verifying The Heater Element Is Getting Ground

3-Wire Oxygen Sensor Heater Test (1994-1995 3.0L Pathfinder and 3.0L Pickup)

Now that you've confirmed that the BLK/WHT of the engine wiring harness connector is feeding the O2 sensor with power...

... The next test is to check that the black with yellow stripe (BLK/YEL) wire (of the engine wiring harness heated O2 sensor's electrical connector) is feeding the heated O2 sensor with ground.

We'll do another simple multimeter voltage test to see if ground is indeed present or not.

IMPORTANT: The pinout in the illustration above is of the connector on the oxygen sensor itself. To check for power, you need to test the BLK/YEL wire of the engine wiring harness sensor connector.

These are the test steps:

  1. 1

    Locate the BLK/YEL wire of the O2 sensor's engine wiring harness connector.

    NOTE: Remember, you'll test the wire that's on the engine wiring harness connector side and NOT on the O2 sensor itself.

  2. 2

    Place your multimeter in Volts DC mode and connect the red multimeter test lead to battery (+).

    Probe the BLK/YEL wire of the O2 sensor's harness connector, with the black multimeter test lead.

  3. 3

    With the Key On, engine Off, this wire should have 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: The BLK/YEL wire has ground due to the fact that the multimeter registered 10 to 12 Volts DC. Good, since this confirms the heated O2 sensor's heater is being fed with ground.

Now that you've checked and confirmed the basics (power and ground), the next step is to check the heater element's resistance with your multimeter...for this test, go to TEST 3: Testing The Heater Element's Resistance.

CASE 2: The BLK/YEL wire DOES NOT have ground due to the fact that the multimeter DID NOT register 10 to 12 Volts DC. Check your connections and repeat the test one more time.

If your multimeter still doesn't register the 10 to 12 Volts DC, then the most likely cause of this missing ground is an ‘open’ in the BLK/YEL wire between the O2 sensor's harness connector and the PCM.

TEST 3: Testing The Heater Element's Resistance

3-Wire Oxygen Sensor Heater Test (1994-1995 3.0L Pathfinder and 3.0L Pickup)

Now that you have checked and confirmed that:

  1. The BLK/WHT wire has 10 to 12 Volts DC (TEST 1).
  2. The BLK/YEL wire is feeding the heated O2 sensor with ground (TEST 2).

For our third and last test we're gonna' verify that your Nissan Pathfinder's heated O2 sensor's heater resistance is within factory specification.

NOTE: Just a reminder that the oxygen sensor has to be completely cold before proceeding with this test since the manual calls for the O2 sensor to be at room temperature for the resistance test.

OK, this is what you need to do:

  1. 1

    Locate the O2 sensor terminals A and C of the O2 sensor connector itself (not the engine wiring harness O2 connector).

  2. 2

    With your multimeter in Ohms mode... probe terminals A and C of the O2 sensor itself.

  3. 3

    If all is OK, you should see about 3 to 1000 Ωs on your multimeter.

    If the heater element is fried, your multimeter will show an open (usually indicated by the letters OL) or a number over 10 K Ωs.

Let's take a look at your test results:

CASE 1: The heated O2 sensor's heater resistance is within spec.- This test result tells you that heated oxygen sensor's heater is OK.

CASE 2: Your multimeter showed an open circuit (OL)- This confirms that your Nissan's 3-wire O2 sensor's heater element is fried. Replacing the heated O2 sensor with a new one will solve the P0141 trouble code lighting up the check engine light (CEL).

Here are some more specifics: Since you have:

  1. Confirmed that the heated O2 sensor's heater element is getting power (TEST 1).
  2.      -AND-
  3. Confirmed that the heated O2 sensor's heater element is getting ground (TEST 2).
  4.      -AND-
  5. In this test you have confirmed that the heater element's resistance is out of specification.

Taking all of the above into account you can correctly conclude that the heated O2 sensor, on your Pathfinder (or Pick Up) needs to be replaced with a new one.