O2 Sensor #2 Heater Element Test (1994 3.0L Ford Ranger And Mazda B3000)

TEST 2: Making Sure That Ground Is Present

Now that you've confirmed that the O2 sensor's heater is getting power, we need to make sure that it has Ground.

The wire that supplies Ground to the O2 sensor's heater is the black with white stripe (BLK/WHT) wire or black (BLK) wire of the engine wiring harness O2 sensor connector.

These are the test steps:

1. 1

   Locate oxygen sensor #2 and disconnect it from its harness connector.

2. 2

   Locate the black with white stripe (or black) wire of the engine wiring harness oxygen sensor connector.

3. 3

   With your multimeter in Volts DC mode, probe the BLK/WHT (or BLK) wire with the black multimeter test lead.
   
   Connect the red multimeter test lead directly on the battery's positive (+) terminal.

4. 4

   Your multimeter should register 10 to 12 Volts DC if Ground is present.

Let's take a look at your test results:

CASE 1: The O2 sensor's heater is getting Ground. This is the correct test result.

So far, your tests have confirmed that the #2 O2 sensor's heater has everything it needs to activate. The next step now is to check its resistance. For this test go to: TEST 3: Testing The Resistance Of The Heater Element.

CASE 2: The O2 sensor's heater IS NOT getting Ground. This lack of Ground will cause the heater to not activate.

The most likely cause of this missing Ground is an open in the black with white stripe wire between the O2 connector and your vehicle's chassis.

Your next step is to repair and restore this Ground so that the O2 sensor's heater will work again.

The following circuit diagram of the oxygen sensor will help you further diagnose the Ground problem: Oxygen Sensor Circuit Diagram (1994 3.0L Ford Ranger And Mazda B3000).

TEST 3: Testing The Resistance Of The Heater Element

For our last test we're going to check the resistance of the #2 oxygen sensor's heater element.

This is a very simple test that's done with a multimeter in Ohms mode.

This test is done on the connector of the O2 sensor itself. As you can see in the photo above, this connector has round male terminals.

Let's get started:

1. 1

   Locate the O2 sensor terminals number 1 and number 2 of the O2 sensor connector itself (not the engine wiring harness O2 connector).

2. 2

   With your multimeter in Ohms mode probe terminals number 1 and number 2 of the O2 connector.

3. 3

   If all is OK, you should see about 5 to 30 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 resistance test result:

CASE 1: The heater element's resistance is within specification. This is the correct test result.

You can conclude that the O2 sensor #2's heater is functioning correctly if its resistance is within specification and it's getting power and Ground.

CASE 2: The heater element's resistance IS NOT within specification. This tells you that the O2 sensor is defective and needs to be replaced.

More 3.0L Ford Ranger Tutorials

You can find a complete list of 3.0L Ford Ranger tutorials in this index:

• Ford 3.0L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• Tune Up And Torque Specifications 1991-1994 3.0L Ford Ranger.
• How To Test The TPS (1993-1994 3.0L Ford Ranger).
• How To Test The Fuel Injectors (1992-1994 3.0L Ford Ranger).
• How To Test The Fuel Injectors (1992-1994 3.0L Ford Ranger) (at: troubleshootmyvehicle.com).