Testing The Oxygen Sensor 1 Heater (2002-2003 2.5L Nissan Altima)

This tutorial will help you to test the front O2 sensor heater on the 2000-2003 2.5L Nissan Altima.

Testing the front O2 sensor's heater involves making sure that the heater is getting power and then testing its internal resistance.

All of the test steps are explained in a step-by-step manner and you can also find the O2 sensor wiring diagram here: Heated Oxygen Sensor 1 Circuit Diagram.

Symptoms Of A Defective O2 Sensor 1 Heater

When the O2 sensor fails you're gonna' have a trouble code lighting up a check engine light on your Nissan Altima's instrument cluster.

You're gonna' see one of the following trouble codes registered in your Nissan Altima PCM's memory:

  1. P0031: Front Heated Oxygen Sensor Heater 1 Circuit Low Input.
  2. P0032: Front Heated Oxygen Sensor Heater 1 Circuit High Input.

Front O2 Sensor Basics

Testing The Oxygen Sensor 1 Heater (2002-2003 2.5L Nissan Altima)

The O2 sensor's heater is tasked with heating up the O2 sensor as soon as the engine starts and keeping it hot even when the engine is running (especially at idle).

All of this is so that the O2 sensor can start sensing the oxygen content of the exhaust and control emissions as soon as the engine starts and while it's running.

As you're probably already aware, the front O2 sensor has 4 wires sticking out of its connector.

To test the O2 sensor #1's heater, we need to know which wire supplies it with power.

We also need to know which terminals, of the connector of the O2 sensor itself, are part of the heater element circuit inside the O2 sensor.

2002-2003 2.5L Nissan Altima
Pin Wire Color Description
1 WHT O2 Signal (PCM)
2 ORG/BLK Heater (PCM)
3 RED/YEL Heater Power (+)
4 BLK Ground (-)

You can see these wires in the O2 sensor wiring diagram here: Heated Oxygen Sensor 1 Circuit Diagram.

TEST 1: Making Sure The O2 Sensor Heater Is Getting Power

Making Sure The O2 Sensor Heater Is Getting Power. Testing The Oxygen Sensor 1 Heater (2002-2003 2.5L Nissan Altima)

The O2 sensor #1's heater needs 12 Volts to activate. So our first test we're going to make sure sure that the O2 sensor is getting power.

This power comes from fuse #15 (15 amp) of your 2002-2003 2.5L Nissan Altima's dash fuse box. The wire that carries these 12 Volts to the O2 sensor is the red with yellow stripe (RED/YEL) wire.

We'll use a multimeter to check for these 12 Volts.

CAUTION: Since the O2 sensor is located in the exhaust stream, it can get very hot when the engine is running. It can stay very hot even after the engine has been turned off. Let the engine cool down completely before attempting any of the tests. Be careful and take all necessary safety precautions.

NOTE: This test is done on the O2 sensor connector that belongs to the engine wiring harness. This connector has female terminals.

These are the test steps:

  1. 1

    Disconnect the front O2 sensor from its electrical connector.

  2. 2

    Place your multimeter in Volts DC.

  3. 3

    Connect the red multimeter test lead to the RED/YEL wire.

  4. 4

    Connect the black multimeter test lead directly to the battery negative (-) terminal.

  5. 5

    Turn the key on but don't crank or start the engine.

  6. 6

    The multimeter should read 10 to 12 Volts DC.

    Turn the key off when done.

Let's take a look at your test results:

Let's examine your test results:

CASE 1: The RED/YEL wire has 10 to 12 Volts.. This is the correct and expected test result.

Now that you've confirmed that your Altima's O2 sensor's heater is getting power, the next step is to make sure that it's getting ground. For this test go to: TEST 2: Testing The Heater Element's Resistance.

CASE 2: The RED/YEL wire does not have 10 to 12 Volts.. Without power the front O2 sensor's heater will not activate.

The most likely cause of this missing power is a blown fuse. Check that the #15 dash fuse box fuse is not blown.