When the front O2 sensor's internal heater fails, the PCM will set a diagnostic trouble code P0135. But an internal heater failure isn't the only thing that'll set the trouble code.
In this tutorial, I'm going to share with you how to test the heater with a multimeter. I'm also gonna show you how to make sure the heater is getting power and Ground.
Your test result will quickly confirm what is causing the P0135 trouble code.
Contents of this tutorial:
- Circuit Descriptions Of The Upstream Oxygen Sensor.
- Where To Buy The Oxygen Sensor And Save.
- TEST 1: Making Sure The Heater Element Is Getting Power.
- TEST 2: Making Sure The Heater Element Is Getting Ground.
- TEST 3: Testing The Heater Element's Resistance.
- Oxygen Sensor Fuse Location.
- More 3.1L V6 Buick, Oldsmobile Tutorials.
APPLIES TO: This tutorial applies to the following vehicles:
- 3.1L V6 Buick Century: 1997, 1998, 1999.
- 3.1L V6 Buick Skylark: 1997, 1998.
- 3.1L V6 Oldsmobile Achieva: 1997, 1998.
- 3.1L V6 Oldsmobile Cutlass: 1997, 1998, 1999.
- 3.1L V6 Oldsmobile Cutlass Supreme: 1997.
Circuit Descriptions Of The Upstream Oxygen Sensor
You're probably already aware that the front (upstream) oxygen sensor has four wires sticking out of it.
Two of those four wires connect to the O2 sensor's heater and supply it with 12 Volts and Ground.
Testing the oxygen sensor's heater involves knowing what each wire does.
Here's a brief description of each:
| Upstream Oxygen Sensor (HO2S 1) Pinout | ||
|---|---|---|
| Pin | Wire Color | Description |
| A | Tan (TAN) | O2 Signal Ground |
| B | Purple (PPL) | O2 Signal |
| C | Black (BLK) | Heater Ground (-) |
| D | Brown (BRN) -or- Pink (PNK) | Heater Power (+) |
Where To Buy The Oxygen Sensor And Save
The following known automotive brand name upstream (front) oxygen sensors will fit your 3.1L Buick or Oldsmobile vehicle:
NOTE: If you're not sure if the above O2 sensor fits your particular 3.1L V6 Buick (Oldsmobile), don't worry. Once you get to the site, they'll make sure the sensor is the right one. If not, they'll find you the right one.
TEST 1: Making Sure The Heater Element Is Getting Power
We'll start our diagnostic by making sure that the front O2 sensor's heater receives 10 to 12 Volts.
On the Buick Skylark, Olds Achieva, Olds Cutlass, and Olds Cutlass Supreme, the wire that supplies 12 Volts to the front O2 sensor is the brown (BRN) wire of the O2 sensor's engine wiring harness connector.
On the Buick Century, the wire that supplies 12 Volts to the front O2 sensor is the pink (PNK) wire of the O2 sensor's engine wiring harness connector.
On all vehicles, the BRN or PNK wire connects to the female terminal labeled with the letter D in the illustration above.
CAUTION: The oxygen sensor, the catalytic converter, and the exhaust pipe get and stay 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: We're going to be checking for 12 Volts on the O2 sensor's engine wiring harness connector (and not on the connector that belongs to the sensor itself). This connector has female terminals.
OK, these are the steps:
- 1
Locate the upstream oxygen sensor and disconnect it from its harness connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the black multimeter test lead directly on the battery's negative (-) terminal.
- 4
Turn the key to the ON position but don't crank or start the engine.
- 5
Probe the BRN (or PNK) wire with the red multimeter test lead.
The BRN or PNK wire connect to the female terminal labeled with the letter D in the illustration above.
IMPORTANT: If you probe the front of the connector, be careful not to damage the terminal! - 6
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 the correct and expected test result. It lets you know that the front O2 sensor's heater is receiving power.
The next step is to find out if the front O2 sensor's heater is receiving Ground. For this test, go to: TEST 2: Making Sure The Heater Element Is Getting Ground.
CASE 2: The multimeter DID NOT register 10 to 12 V DC. This test result let you know that the front O2 sensor's heater is not receiving power and without it, it will not function.
The most likely cause of this missing power is a blown fuse. Check the O2 sensor's fuse. If the fuse is blown, replace it and repeat the test.
You can find the oxygen sensor fuse location, for your specific vehicle, here: Oxygen Sensor Fuse Location.
