Front O2 Sensor Heater Test -P0135 (1995-1999 1.6 Nissan Sentra)

Oxygen Sensor Heater Test -P0135 (1997-1999 1.6L Nissan Sentra)

Diagnosing a P0135 trouble code on the 1995, 1996, 1997, 1998 and 1999 1.6L Nissan Sentra involves 2 basic tests. One is making sure that the front oxygen sensor is getting power and the other involves a resistance test. Both tests are done with a simple multimeter and I'll show you how in this tutorial.

NOTE: The 1995 and 1996 1.6L Nissan Sentra with Federal Emissions uses a single wire non-heated front oxygen sensor.

In Spanish You can find this tutorial in Spanish here: Calentador del Sensor de Oxígeno Delantero (1995-99 1.6L Sentra) (at:

Circuit Descriptions Of The Upstream Oxygen Sensor

Oxygen Sensor Heater Test -P0135 (1997-1999 1.6L Nissan Sentra)

A trouble code P0135 usually indicates that the front oxygen sensor heater has failed. Why does the O2 sensor need a heater anyway? Because the oxygen sensor needs to reach 600°F (and stay here) to be able to sense the oxygen content of the exhaust stream it's exposed to.

The exhaust gas, while extremely hot, doesn't heat up the O2 sensor fast enough from a cold engine start. It also doesn't keep it hot enough at engine idle. The only way the oxygen sensor's operating temperature can be reached fast and maintained is with an internal heater.

Since the front O2 sensor, on your 1.6L Nissan Sentra, has 3 wires sticking out of it, the table below will help identify the one that we need to test.

TIP: The front oxygen sensor's engine wiring harness connector has female terminals. The connector on the oxygen sensor itself has male spade terminals.

Here's a brief description of the 3 wires of the front oxygen sensor:

Upstream Oxygen Sensor Pinout
(1995-1999 1.6L Nissan Sentra)
Pin Wire Color Description
1 ORG Heater Ground (-)
2 WHT O2 Signal
3 BRN/YEL Heater Power (+)

Where To Buy The Oxygen Sensor And Save Some $$$

If you find that you need to replace the front O2 sensor, I think you'll save a few buck shopping for it with the links below:

NOTE: If you're not sure if the above upstream O2 sensor fits your particular Nissan Sentra, don't worry, once you get to the site, they'll make sure the sensor is the correct one, if not, they'll find you the correct one.

TEST 1: Verifying Power And Ground

Oxygen Sensor Heater Test -P0135 (1997-1999 1.6L Nissan Sentra)

The front O2 sensor's heater element needs power and Ground to work. Power is supplied by the brown with yellow stripe (BRN/YEL) wire of the O2 sensor's engine wiring harness connector.

The O2 sensor's heater gets Ground thru' the orange (ORG) wire of the O2 sensor's engine wiring harness connector.

CAUTION: The oxygen sensor gets and stays very hot even after the engine is off! Perform this test with a completely cold engine. Be careful and take all necessary safety precautions! If you raise your vehicle with a jack, place it on jack stands!

IMPORTANT: The pinout in the illustration above is of the connector on the oxygen sensor itself. To check for power and Ground, you'll test the BRN/YEL wire of the engine wiring harness sensor connector.

OK, this is what you'll need to do:

  1. 1

    Locate the upstream oxygen sensor and disconnect it from its engine wiring harness connector.

  2. 2

    Set your multimeter to Volts DC mode and turn the key ON but don't crank or start the engine (this will power up the O2 sensor's engine wiring harness connector).

  3. 3

    Probe the brown with yellow stripe (BRN/YEL) wire of O2 sensor's connector with your multimeter's red test lead

    Probe the orange (ORG) wire of O2 sensor's connector with your multimeter's black test lead.

    Remember, you're testing the engine wiring harness O2 sensor connector (which has female terminals) and not the connector of the O2 sensor itself.

  4. 4

    With the Key On Engine Off (KOEO), your multimeter should register 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: Your multimeter registered 10 to 12 Volts DC. Good, since this confirms that the front oxygen sensor's heater element is getting power and Ground.

The next step is to verify that the heater's resistance is within specification. For this test, go to: TEST 2: Testing The Heater Element's Resistance.

CASE 2: Your multimeter DID NOT register 10 to 12 Volts DC. The most likely cause is that power is missing due to a blown fuse or a short (or open) in the wiring. You'll need to check fuse #16 (10 amps) in the fuse box and make sure it's not blown.

If the fuse is OK, your next step is to find out why this battery power is missing using a wiring diagram.