The oxygen sensor on the 1993 3.8L equipped GM vehicles is a 3 wire sensor. In this tutorial I'll show you how to test it's internal heater with a simple multimeter.
You don't need any expensive diagnostic test equipment and with the 3 basic diagnostic tests I'm going to show you, you'll find out if the O2 heater is fried or not.
Here are the contents of this tutorial:
- Circuit Descriptions of the Oxygen Sensor.
- TEST 1: Verifying the Heater Element is Getting Power.
- TEST 2: Verifying the Heater Element is Getting Ground.
- TEST 3: Testing the Heater Element's Resistance.
- Where to Buy the Oxygen Sensor and Save Some $$$.
- More 3.8L GM Diagnostic Tutorials.
Puedes encontrar este tutorial en Español aquí: Prueba: Calentador del Sensor de Oxígeno (1993 3.8L V6 GM) (en: autotecnico-online.com).
Circuit Descriptions of the Oxygen Sensor
For the oxygen sensor to start sensing the oxygen content of the exhaust, it has to reach a constant temperature of about 600°F. The exhaust stream, that the O2 sensor is in contact with can't keep it this hot consistently.
To overcome this limitation, the oxygen sensor comes equipped with an internal heater so that it can activate faster (and stay activated) than it would from just the exhaust stream's heat it's exposed to.
Therefore, 2 of the 3 wires feed the heater element with power and ground. The third wire is the one that sends the oxygen content voltage signal to your vehicle's fuel injection computer.
Below, you'll find the color of the wires of the engine wiring harness oxygen sensor connector for the 3-wire oxygen sensor:
|Oxygen Sensor Pinout (1993 3.8L V6 GM)|
|A||PNK/BLK||Heater Power (+)|
|B||BLK||Heater Ground (-)|
NOTE: The connector in the illustration (that I'm using in this tutorial) is of the connector on the oxygen sensor itself. The connector on the O2 sensor itself has male spade terminals.
TEST 1: Verifying the Heater Element is Getting Power
Your 1993 3.8L equipped GM vehicle's oxygen sensor gets power (12 Volts DC) from a fuse in the under-dash fuse block.
These 12 Volts are then sent to the 3-wire O2 sensor thru' the pink with black stripe (PNK/BLK) wire of the engine wiring harness oxygen sensor connector.
To check for these 12 Volts, we need to do a simple multimeter voltage test.
CAUTION: The oxygen sensor gets and stays very hot even after the engine is off! Perform this test with a completely cold engine. Be careful and take all necessary safety precautions! If you raise your vehicle with a jack, place it on jack stands!
IMPORTANT: The illustration above is of the connector on the oxygen sensor itself. To check for power, you need to test the PNK/BLK wire of the engine wiring harness sensor connector.
OK, this is what you'll need to do:
Locate the 3-wire oxygen sensor and disconnect it from its harness connector.
Locate the PNK/BLK wire of the engine wiring harness oxygen sensor connector.
With your multimeter in Volts DC mode, probe the PNK/BLK with the red multimeter lead.
Ground the black multimeter lead directly on the battery's negative terminal.
With the Key On Engine Off (KOEO), the RED wire should have 10 to 12 Volts DC.
Let's take a look at your test results:
CASE 1: The PNK/BLK wire has 10 to 12 Volts DC- Good, since this confirms that the 3-wire oxygen sensor's heater element is getting power.
The next step is to make check that the black (BLK) wire, of the O2 sensor engine wiring harness connector, is feeding ground to the heater element. For this test, go to TEST 2: Verifying the Heater Element is Getting Ground.
CASE 2: The PNK/BLK wire DOES NOT have 10 to 12 Volts DC- Re-check that you're testing the correct wire and that the Key is in the RUN position (but don't crank or start the engine) and re-test.
If you still don't see 10 to 12 Volts DC... then this test result tells you that the 3-wire oxygen (O2) sensor itself IS NOT BAD... since without power, the heater element won't work.
Although it's beyond the scope of this article... the next step is to find out why this battery power is missing using a wiring diagram.