O2 Sensor #1 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 LT BLU/ORG wire is feeding the heater with power, the next step is to check that the black with white stripe (BLK/WHT) (or black) wire is providing Ground.

This Ground wire connects directly to your Ford Ranger's chassis and should be present at all times (either with the key on or key off).

NOTE: This test is done on the engine wiring harness connector. This connector has round female terminals.

These are the test steps:

1. 1

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

2. 2

   Locate the BLK/WHT (or BLK) wire of the engine wiring harness oxygen sensor connector.

3. 3

   With your multimeter in Volts DC mode, probe the BLK/WHT (or BLK) 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 BLK/WHT (or BLK) wire is feeding Ground to the heater. This is the correct test result.

Now that you know that the heater is getting power and Ground, the next step is to check the O2 sensor's heater resistance with your multimeter in Ohms mode. For this test go to: TEST 3: Testing The Resistance Of The Heater Element.

CASE 2: The BLK/WHT (or BLK) wire IS NOT feeding Ground to the heater. Without this Ground, the heater element won't activate.

This usually means that the Ground wire is open between the O2 sensor connector and the chassis. Repairing the Ground wire will solve the 'no-Ground' issue. The following circuit diagram may be of help: Oxygen Sensor Circuit Diagram (1994 3.0L Ford Ranger And Mazda B3000).

TEST 3: Testing The Resistance Of The Heater Element

Now that you have confirmed that the right front O2 sensor is getting power and Ground, we are going to test the resistance of the heater itself.

So far, all of your tests have been done on the engine wiring harness connector which has round female terminals. This test is going to be done on the connector of the O2 sensor itself. And this bad boy has round male terminals.

The resistance specification of the internal heater is 5 to 30 Ohms.

1. 1

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

2. 2

   With your multimeter in Ohms mode, probe terminals 1 and 2 of the O2 sensor itself.

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 test results:

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

Since you have confirmed that the heater's resistance is within specification and that it is getting both power and Ground, you can conclude that the O2 sensor's heater is not defective.

CASE 2: The heater element resistance IS NOT within specification. This test result lets you know that the oxygen 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 Pump (1992-2000 3.0L Ford Ranger) (at: troubleshootmyvehicle.com).