TEST 1: Checking For 12 Volts (Pink Wire)
NOTE: Before you start testing, just a friendly reminder: Perform all tests with a cold engine to avoid serious burns on your hands and/or fingers.
OK, The very first thing you need to do, is to make sure that the front oxygen sensor on your 3.8L Buick (Chevy, Olds, or Pontiac) is getting power.
You can use 12 Volt automotive test light or a multimeter for this test and TEST 2 but to make sure that you're getting the right amount of voltage, I recommend using a multimeter. If you don't have one or need to upgrade yours, check out my recommendation here: Buying A Digital Multimeter For Automotive Diagnostic Testing at: easyautodiagnostics.com).
OK, to get our P0135 DTC troubleshooting under way, this is what you need to do:
- Locate the upstream oxygen sensor and disconnect it from its electrical connector.
- Locate the Pink wire of the engine wiring harness oxygen sensor connector.
- The letter D will be embossed on the connector.
- With your multimeter in Volts DC mode:
- With the red multimeter lead, probe the letter D wire of the engine wiring harness connector (this will be the pink wire).
- Ground the black multimeter lead.
- With the key ON, engine OFF, this wire should have 10 to 12 Volts DC.
Let's take a look at your test results:
CASE 1: Your multimeter recorded 10 to 12 Volts DC. This is good and let's you know that the O2 sensor fuse is good and supplying power to the upstream O2 sensor.
The next step is to make sure that the oxygen sensor's heater element is getting a good Ground on the C circuit wire. For this test, go to: TEST 2: Checking Ground (Circuit C Wire).
CASE 2: Your multimeter DID NOT record the indicated voltage. This usually means that the O2 sensor fuse is blown.
Check the O2 sensor fuse and replace if necessary and retest.
TEST 2: Checking Ground (Circuit C Wire)
As mentioned earlier in this tutorial, the heater element inside the oxygen sensor needs Ground to activate.
The wire labeled with the letter C is the one that supplies this Ground to the sensor's heater.
In this test section, you'll check this Ground much the same way you tested for power.
This is what you'll need to do:
- Disconnect the rear sensor sensor (if it isn't already from TEST 1).
- Locate the circuit C.
- You'll test the wire that is on the engine wiring harness connector side.
- Place your multimeter in Volts DC mode and:
- Connect the red multimeter test lead to battery (+).
- Connect the black multimeter test lead to the C circuit wire of the engine wiring harness connector side.
- With the key ON, engine OFF, this wire should have 10 to 12 Volts DC.
Let's take a look at your test results:
CASE 1: The multimeter registered 10 to 12 Volts DC. Good deal, with this test result, we now know that the O2 sensor is getting Ground.
Now that we have confirmed that the O2 sensor connector is feeding both power and Ground, the next and final test, is to see if the heater element itself is bad or not. This is a simple test that requires you to check the heater element's resistance with your multimeter. For this test, go to: TEST 3: O2 Heater Resistance Test.
CASE 2: The multimeter DID NOT register 10 to 12 Volts DC. Re-check all of your connections and make sure you're testing the correct wire.
If your multimeter still does not indicate the 10 to 12 Volts DC, the black wire has an open-circuit problem.
By an open-circuit, I mean that the wire is cut somewhere between it and its Ground point. To confirm this, you can use a jumper wire to Ground this circuit and repeat the test.
Repairing this Ground issue will solve the P0135 issue you're having with your 3.8L Buick (Chevy, Olds, or Pontiac) vehicle.
