TEST 2: Verifying The Heater Element Is Getting Ground

Oxygen Sensor Heater Test -P0135 (1998-2000 2.5L Stratus/Cirrus)

The black (BLK) wire of the engine wiring harness O2 sensor connector is the one that feeds ground to the upstream oxygen sensor.

We'll do a simple multimeter voltage test to confirm that the BLK wire is feeding the O2 sensor's heater element with ground.

NOTE: The illustration above is of the connector on the oxygen sensor itself. To test for the heater element ground you need to test the BLK wire of the engine wiring harness sensor connector.

These are the test steps:

  1. 1

    Locate the BLK wire of the O2 sensor's engine wiring harness connector.

    NOTE: Remember, you'll test the wire that's on the engine wiring harness connector side and NOT on the O2 sensor itself.

  2. 2

    Place your multimeter in Volts DC mode and connect the red multimeter test lead to battery (+).

    Probe the BLK wire of the O2 sensor's harness connector, with the black multimeter test lead.

  3. 3

    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. This test result lets you know that the upstream oxygen sensor's heater element is getting ground on your 2.5L V6 Stratus (Cirrus).

So far you've confirmed that the upstream O2 sensor's heater element is getting both power and ground. The next step is to check the heater element's resistance with your 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. Re-check all of your connections and make sure you're testing the correct terminal.

If your multimeter still doesn't register the 10 to 12 Volts DC, then the most likely cause of this missing ground is an ‘open’ in the BLK wire between the chassis connector and the O2 sensor's harness connector.

TEST 3: Testing The Heater Element's Resistance

Oxygen Sensor Heater Test -P0135 (1998-2000 2.5L Stratus/Cirrus)

Now that you have verified that power and ground is available to the upstream oxygen sensor on your 1998-2000 Stratus (Cirrus), the next and last test is to check the resistance of the heater element itself.

We can measure the resistance with the multimeter set to Ohms () mode. If the resistance is not within specification, then we now know the O2 sensor is bad and the cause of the P0135: O2 Sensor 1/1 Heater Failure trouble code.

NOTE: Test the upstream oxygen sensor with a completely cold engine to avoid burns!

OK, this is what you need to do:

  1. 1

    Locate the O2 sensor terminals number 1 and number 2 of the O2 sensor connector itself (not the engine wiring harness O2 connector).

    NOTE: You can use the illustration above since it identifies the terminals on the connector of the oxygen sensor itself.

  2. 2

    With your multimeter in Ohms mode probe terminals number 1 and number 2 of the O2 sensor itself.

  3. 3

    If all is OK, you should see about 4 to 7 Ωs on your multimeter.

    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 take a look at your test results:

CASE 1: Your multimeter confirmed the indicated resistance. This test result tells you that the pre-catalytic converter oxygen (O2) sensor's heater is OK.

CASE 2: Your multimeter showed an open circuit (OL). This confirms that the upstream (Bank 1 Sensor 1) O2 sensor's heater element is fried. Replacing the upstream O2 sensor with a new one will solve the P0135 trouble code lighting up the check engine light (CEL).

Taking into account that you have:

  1. Confirmed that the DK GRN/ORG wire of the engine wiring harness O2 sensor connector has 10 to 12 Volts DC (TEST 1).
  2. Confirmed that the BLK wire of the engine wiring harness O2 sensor connector has ground (TEST 2).
  3. In this test you have confirmed that the heater element's resistance is out of specification.

... You can correctly conclude that the upstream O2 sensor needs to be replaced with a new one.