In this tutorial, I'll show you how to test the front oxygen sensor's heater element with a multimeter.
With your test results you'll able to find out it's bad and behind the trouble code P0135 lighting up the check engine light on your 1996 4.0L Jeep Cherokee.
I'm also going to tell you where you can buy it and save some money.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Calentador Del Sensor De Oxígeno Delantero (1996 4.0L Jeep Cherokee) (at: autotecnico-online.com).
APPLIES TO: This oxygen sensor heater diagnostic tutorial applies to the following vehicles:
- 1996 4.0L Jeep Cherokee.
RELATED WIRING DIAGRAMS:
RELATED TUTORIAL:
Circuit Descriptions Of The Upstream Oxygen Sensor
The front oxygen sensor is located before the catalytic converter (as such, it's also known as the upstream O2 sensor -upstream from the catalytic converter).
Here's a brief description of the 4 wires coming out of the front heated oxygen sensor.
NOTE: The front oxygen sensor's engine wiring harness connector has male terminals. The connector on the oxygen sensor itself has female terminals.
| Pin | Wire Color | Description |
|---|---|---|
| 1 | Dark Green With Orange Stripe (DK GRN/ORG) | Heater 12 Volts (+) |
| 2 | Black With White Stripe (BLK/WHT) | Heater Ground (-) |
| 3 | Black With Light Blue Stripe (BLK/LT BLU) | Sensor Ground |
| 4 | Black With Dark Green Stripe (BLK/DK GRN) | O2 Sensor Signal |
For more info on the oxygen sensor circuits, consult this wiring diagram:
Where To Buy The Oxygen Sensor And Save Money
The following links will help you to comparison shop and hopefully save you a few bucks on the purchase of the upstream (front) oxygen sensor.
25%
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
The front O2 sensor's heater element needs 10 to 12 Volts DC to activate and start heating.
The wire that supplies this voltage to the heater is the dark green with orange stripe (DK GRN/ORG) wire of the O2 sensor's 4-wire engine wiring harness connector.
We'll do a simple multimeter voltage test on the DK GRN/ORG wire to check for the presence of these 12 Volts.
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
Disconnect the front O2 sensor from its engine wiring harness connector.
NOTE: The O2 sensor's engine wiring harness connector has male terminals. - 2
Set your multimeter to Volts DC mode.
- 3
Turn the key to the ON position but don't crank or start the engine.
- 4
Connect the black multimeter test lead to the battery negative (-) terminal.
- 5
With the red multimeter test lead, probe the male terminal that connects to the DK GRN/ORG wire.
NOTE: This is the male terminal of the engine wiring harness connector. - 6
Your multimeter should read 10 to 12 Volts DC.
Let's take a look at your test results:
CASE 1: The DK GRN/ORG wire is providing 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 DK GRN/ORG wire IS NOT providing 10 to 12 Volts DC. Without these 10 to 12 Volts the O2 sensor's heater will not function.
An open-circuit problem in the DK GRN/ORG wire, between the O2 sensor connector and the auto shutdown (ASD) relay, is usually the most common cause of this missing voltage.