TEST 2: Checking The Heater Ground

P0135 Oxygen Sensor 1996-2001 3.9L, 5.2L, 5.9L Dodge Ram

Now that you've verified that your Dodge Ram's upstream O2 sensor's heater is getting power on the DK GRN/ORG (dark green w/ orange stripe) wire.

The next step is to verify that the BLK/WHT (black w/ white stripe) wire is feeding the heater with Ground.

To confirm this Ground, you'll do a simple voltage test with your multimeter.

These are the test steps:

  1. 1

    Disconnect the oxygen sensor (if it isn't already from TEST 1).

  2. 2

    Locate the wire that connects to terminal number 2 of the O2 sensor's harness connector.

    1. This is usually a BLK/WHT (black w/ white stripe) wire.
    2. You'll test the wire that's on the engine wiring harness connector side and NOT on the O2 sensor itself.
  3. 3

    Place your multimeter in Volts DC mode and:

    1. Connect the red multimeter test lead to battery (+).
    2. Connect the black lead to terminal number 2 of the O2 sensor's harness connector.
  4. 4

    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 result tells you that the upstream O2 sensor heater, on your Dodge Ram, is getting Ground.

The next (and last) step is to see if the O2 sensor heater element's resistance is within factory specifications. 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, then the BLK/WHT wire has an ‘open’.

By an ‘open’, 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 Dodge Ram.

TEST 3: O2 Heater Resistance Test

P0135 Oxygen Sensor 1996-2001 3.9L, 5.2L, 5.9L Dodge Ram

Alright, you've come to the final test. So far, you have:

One: The upstream oxygen (O2) sensor's heater element is getting power (10 to 12 Volts DC) on the DK GRN/ORG wire of the O2 sensor's harness connector (in TEST 1).

Two: In TEST 2, you confirmed that the BLK/WHT wire is feeding the heater element with Ground.

NOTE: The manual calls for the O2 sensor to be at room temperature for the resistance test, so make sure the O2 sensor is completely cold (as in a cold engine).

These are the test steps:

  1. 1

    Disconnect the upstream oxygen sensor from the engine wiring harness connector (if it isn't already from the previous tests).

    1. NOTE: The O2 sensor must be disconnected from the vehicle's connector for this test!
  2. 2

    Locate the O2 sensor terminals number 1 and number 2.

  3. 3

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

    1. NOTE: Remember, you're testing the oxygen sensor itself.
    2. If all is OK, you should see about 4 to 7 Ωs.
    3. If the heater element is fried, your multimeter will show an open (usually indicated by the letters OL).

Let's take a look at your test results:

CASE 1: Your multimeter confirmed the indicated resistance- This multimeter 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. Replace the upstream O2 sensor with a new one.

A new upstream oxygen sensor will solve the P0135 diagnostic trouble code that is illuminating the check engine light on your Dodge Ram.

NOTE: If you'd like to save a few bucks (and sometimes a whole more!) on the oxygen sensor for your Dodge, check out my recommendation on where to buy it in the next page.



Dodge Vehicles:

  • Ram 1500 Pickup 3.9L, 5.2L, 5.9L
    • 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001
  • Ram 2500 Pickup 5.2L, 5.9L
    • 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001
  • Ram 3500 Pickup 5.9L
    • 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001