How To Test The Oxygen Sensor's Heater (1993, 1994, 1995 4.0L Jeep Cherokee)

The oxygen sensor, on the 1993-1995 4.0L Jeep Cherokee, is a 4 wire sensor that comes equipped with an internal heater.

Sooner or later the O2 sensor's internal heater will fail and the fuel injection computer will set an oxygen sensor trouble code.

In this tutorial I'm going to explain how to test the heater element of the O2 sensor and I'm also going to tell you where you can buy it and save some money.

En Español You can find this tutorial in Spanish here: Cómo Probar El Calentador Del Sensor De Oxígeno (1993-1995 4.0L Jeep Cherokee) (at: autotecnico-online.com).

APPLIES TO: This oxygen sensor heater diagnostic tutorial applies to the following vehicles:

  1. 1993, 1994, 1995 4.0L Jeep Cherokee.

RELATED WIRING DIAGRAMS:

  1. Oxygen Sensor Circuit Wiring Diagram (1993-1995 4.0L Jeep Cherokee).

Circuit Descriptions Of The Oxygen Sensor

Circuit Descriptions Of The Oxygen Sensor. How To Test The Oxygen Sensor's Heater (1993, 1994, 1995 4.0L Jeep Cherokee)

Here's a brief description of the 4 wires coming out of the oxygen sensor.

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

Pin Wire Color Description
1 Black With Light Blue Stripe (BLK/LT BLU) Sensor Ground
2 Black With Dark Green Stripe (BLK/DK GRN) O2 Sensor Signal
3 Dark Green With Black Stripe (DK GRN/BLK) Heater 12 Volts (+)
4 Black With Tan Stripe (BLK/TAN) Heater Ground (-)

For more info on the oxygen sensor circuits, consult this wiring diagram:

  1. Oxygen Sensor Circuit Wiring Diagram (1993-1995 4.0L Jeep Cherokee).

Where To Buy The Oxygen Sensor And Save Money

The O2 sensor isn't an expensive component and it's one that you can find just about at any auto parts store. The following links will help you to comparison shop and hopefully save you a few bucks.

NOTE: If you're not sure if the above upstream O2 sensor fits your particular 4.0L Jeep Cherokee, don't worry, once you get to the site, they'll make sure the sensor fits, if not, they'll find you the correct one.

TEST 1: Making Sure The Heater Is Getting 12 Volts

Making Sure The Heater Is Getting 12 Volts. How To Test The Oxygen Sensor's Heater (1993, 1994, 1995 4.0L Jeep Cherokee)

The first thing we're gonna' do, to get our diagnostic under way, is to make sure that the O2 sensor's heater element is getting 12 Volts DC.

The wire that supplies this voltage to the O2 sensor is the dark green with black stripe (DK GRN/BLK) wire of the O2 sensor's 4-wire connector (of the engine wiring harness).

To find out if 12 Volts are present in the DK GRN/BLK wire, we're gonna' do a simple multimeter voltage test.

IMPORTANT: Perform this and all O2 sensor tests with a completely cold engine! If you have to raise your vehicle to access the O2 sensor, use jack stands. Be careful and think safety all of the time.

OK, these are the test steps:

  1. 1

    Disconnect the O2 sensor from its engine wiring harness connector.

    NOTE: The O2 sensor's engine wiring harness connector has female terminals.

  2. 2

    Set your multimeter to Volts DC mode.

  3. 3

    Turn the key to the ON position but don't crank or start the engine.

  4. 4

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

  5. 5

    With the red multimeter test lead, gently probe the female terminal that connects to the DK GRN/BLK wire.

    NOTE: This is the female terminal of the engine wiring harness connector.

  6. 6

    Your multimeter should read 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: Your multimeter registered 10 to 12 Volts DC. This is the correct and expected test result.

The next step is to make sure that the O2 sensor's heater element is getting Ground. For this test go to: TEST 2: Making Sure The Heater Is Getting Ground.

CASE 2: The O2 sensor's heater is not getting power. Without these 10 to 12 Volts the O2 sensor's heater will not function.

The most likely cause of this missing voltage is an open-circuit problem in the DK GRN/BLK wire. Between the O2 sensor connector and the fuel pump relay.

Your next step is to check the continuity of the DK GRN/BLK wire between the O2 sensor's connector and the fuel pump relay socket in the Power Distribution Center.

Jeep Vehicles:

  • Cherokee 4.0L
    • 1993
      1994
      1995