Even though the 1994 3.0L V6 Ford Ranger (Mazda B3000) is OBD 1 equipped, it comes equipped with 2 heated oxygen sensors.
In this tutorial I'll explain how to make sure that the O2 sensor #1 (which is the O2 sensor for Bank 1) is getting power and Ground and how to test the resistance of the heater element itself.
Contents of this tutorial at a glance:
You can find this tutorial in Spanish here: Calentador Del Sensor De Oxígeno N.º 1 (1994 3.0L Ford Ranger) (at: autotecnico-online.com).
You can find the 1994 3.0L Ford Ranger (Mazda B3000) oxygen sensor #2 heater test here: O2 Sensor #2 Heater Element Test (1994 3.0L Ford Ranger And Mazda B3000).
NOTE: You can find the oxygen sensor circuit diagram here: Oxygen Sensor Circuit Diagram (1994 3.0L Ford Ranger And Mazda B3000).
Heated Oxygen Sensor #1 Basics
As you're probably already aware, your 3.0L Ford Ranger (Mazda B3000) comes equipped with a total of 2 oxygen sensors. Both have internal heaters that help them activate faster.
Sooner or later the internal heater is going to fail. But because the 1994 3.0L V6 Ford Ranger is OBD1 equipped, the fuel injection computer will not register a trouble code to let you know.
The cool thing is that testing the oxygen sensor's heater involves making sure it's getting power and Ground. And then testing the heater's internal resistance to see if it's within specification. In this tutorial I'll explain how to do these 3 tests in a step-by-step way.
TEST 1: Making Sure That Power Is Present
As you're probably already aware, the right front oxygen sensor has 4 wires coming out of the connector.
The connector on the O2 sensor itself has male spade terminals. While the connector of the engine wiring harness has female terminals.
The wire that feeds power to the front right O2 sensor's heater is the light blue with orange stripe (LT BLU/ORG) wire of the engine wiring harness harness O2 sensor connector.
CAUTION: Perform all tests with a completely cold engine!
NOTE: This test is done on the engine wiring harness connector. This connector has round female terminals.
Let's get testing:
Disconnect the right front O2 sensor from its harness connector.
Locate the light blue with orange wire (LT BLU/ORG) of the engine wiring harness oxygen sensor connector.
With your multimeter in Volts DC mode, probe the LT BLU/ORG wire with the red multimeter test lead.
Ground the black multimeter test lead directly on the battery's negative (-) terminal.
With the Key On Engine Off (KOEO), the LT BLU/ORG wire should have 10 to 12 Volts DC.
Let's take a look at your test results:
CASE 1: Power is present in the LT BLU/ORG wire. This is the correct and expected test result.
The next step is to see if the BLK/WHT wire is feeding Ground to the right front O2 sensor's heater. For this test go to: TEST 2: Making Sure That Ground Is Present.
CASE 2: Power is not present in the LT BLU/ORG wire. Without these 10 to 12 Volts, the O2 sensor's heater is not gonna' work.
A lack of power in the LT BLU/ORG wire usually means that the #18 fuse in the dash fuse box is blown. Your next step is to check the #18 fuse and replace if blown.
The following circuit diagram of the oxygen sensor's on your 1994 3.0L Ford Ranger (Mazda B3000) will help you further diagnose these missing 12 Volts: Oxygen Sensor Circuit Diagram (1994 3.0L Ford Ranger And Mazda B3000).