Front O2 Sensor Heater Tests (1997-1999 3.1L V6 Buick, Oldsmobile)

TEST 2: Making Sure The Heater Element Is Getting Ground

So far, in TEST 1, you confirmed that the O2 sensor's heater is receiving power. In this test section, we'll make sure that it's receiving Ground.

The wire that delivers Ground to the front O2 sensor's heater is the black (BLK) wire of the O2 sensor's engine wiring harness connector.

The BLK wire connects to the female terminal labeled with the letter C in the illustration above.

The Ground that the BLK wire delivers to the O2 sensor's heater is a chassis Ground, which means that this wire connects directly to the chassis or engine on your 3.1L Buick or Oldsmobile.

A multimeter voltage test will help us determine if the BLK wire delivers Ground to the O2 sensor's heater.

IMPORTANT: We'll check for Ground on the O2 sensor's engine wiring harness connector (not on the connector that belongs to the sensor itself). This connector has female terminals.

These are the test steps:

1. 1

   Disconnect the O2 sensor's connectors.

2. 2

   Place your multimeter in Volts DC mode.

3. 3

   Connect the red multimeter test lead directly on the battery's positive (+) terminal.

4. 4

   Probe the BLK wire with the black multimeter test lead.
   
   The BLK wire connects to the female terminal labeled with the letter C in the illustration above.
   
   IMPORTANT: If you probe the front of the connector, be careful not to damage the terminal!

5. 5

   You should see 10 to 12 Volts on your multimeter.

Let's take a look at your test results:

CASE 1: The multimeter registered 10 to 12 Volts DC. This is good, since it indicates that the front O2 sensor's heater element is receiving Ground.

The next and last test is to check the heater element's resistance with the multimeter. For this test, go to: TEST 3: Testing The Heater Element's Resistance.

CASE 2: The multimeter DID NOT register 10 to 12 Volts DC. This test result tells you that the O2 sensor's heater element is not receiving Ground.

The most likely cause of this missing Ground is an open-circuit problem in the ? Wire between the O2 sensor's harness connector and chassis Ground.

TEST 3: Testing The Heater Element's Resistance

So far, the results from the previous two tests have confirmed that:

• The O2 sensor's heater element is receiving 10 to 12 Volts DC (TEST 1).
• The O2 sensor's heater element is receiving Ground (TEST 2).

We'll now check the heater element's resistance and see if it's within specification (3 to 10 Ohms). If it isn't, we can conclude that the heater element is bad and that the front O2 sensor needs replacement.

NOTE: The manual calls for the O2 sensor to be at room temperature for the resistance test. If the sensor is hot, let it cool down completely before testing its resistance.

IMPORTANT: We'll perform the test on the connector that belongs to the O2 sensor itself. This connector has male spade terminals (see illustration above).

Let's get started:

1. 1

   Locate the O2 sensor female terminals C and D of the O2 sensor connector itself (not the engine wiring harness O2 connector).

2. 2

   Place your multimeter in Ohms mode.

3. 3

   Measure the resistance across male terminals C and D of the O2 sensor itself with the multimeter test leads.

4. 4

   You should see about 3 to 10 Ωs on your multimeter (you'll typically see about 5 Ohms).
   
   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 interpret your test results:

CASE 1: The front O2 sensor's heater resistance is within specification. This is the correct and expected test result and it lets you know that the O2 sensor's heater element is OK.

CASE 2: Your multimeter showed an open circuit (OL). This test result lets you know that the heater element is bad.

You can correctly conclude that the front O2 sensor is bad and needs replacement if you have:

• Confirmed that the front O2 sensor's heater element is getting power (TEST 1).
• Confirmed that the front O2 sensor's heater element is getting Ground (TEST 2).
• In this test, you have confirmed that the heater element's resistance is not within specification.

Oxygen Sensor Fuse Location

O2 sensor fuse locations:

• 1997-1999 3.1L V6 Buick Century:
  • Oxygen Fuse. Underhood Electrical Center (1997-1998).
  • Oxygen Fuse. Underhood Accessory Junction Box (1999).

• 1997-1998 3.1L V6 Buick Skylark:
  • O2 Fuse. Instrument Panel (I/P) Fuse Block.

• 1997-1998 3.1L V6 Oldsmobile Achieva:
  • O2 Fuse. Instrument Panel (I/P) Fuse Block.

• 1997-1999 3.1L V6 Oldsmobile Cutlass:
  • ERLS Fuse. Underhood Bussed Electrical Center (Underhood Junction Block).

• 1997 3.1L V6 Oldsmobile Cutlass Supreme:
  • ECM IGN Fuse. Underhood Electrical Center #1.

More 3.1L V6 Buick, Oldsmobile Tutorials

You can find a complete list of 3.1L V6 Buick (Oldsmobile) tutorials in this index:

• GM 3.1L Index Of Articles.

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

• How To Test Engine Compression Test (3.1L V6 Buick, Oldsmobile).
• How To Test A Blown Head Gasket (3.1L V6 Buick, Oldsmobile).
• How To Test The Fuel Pump (3.1L V6 Buick, Oldsmobile).
• How To Test The 24X Crankshaft Position Sensor (1995-1997 3.1L V6 Oldsmobile Cutlass Supreme).