TEST 2: Verifying The Heater Element Is Getting Ground

Front Oxygen Sensor Heater Test -P0135 (1998-2002 1.8L Toyota Corolla)

So far you've checked and confirmed that the upstream O2 sensor's heater is being fed battery power by the BLK wire... now, in this test section, we need to make sure that it's being fed ground.

The wire that feeds the upstream O2 sensor's heater with ground is the pink PNK wire (of the engine wiring harness upstream O2 sensor's electrical connector).

We'll check for ground by doing a simple multimeter voltage test very much like the one we did in TEST 1.

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

These are the test steps:

  1. 1

    Locate the PNK 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 PNK wire of the O2 sensor's harness connector.

  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 showed 10 to 12 Volts DC- This tells you that ground IS NOT missing.

Now that you've made sure the upstream O2 sensor's heater element is getting both power and ground... our next step is to check the heater element's resistance with your multimeter. Go to: TEST 3: Testing The Heater Element's Resistance.

CASE 2: The multimeter DID NOT show 10 to 12 Volts DC- Re-check all of your connections and make sure you're testing the correct terminal.

If you still don't see 10 to 12 Volts DC, then the most likely cause of this missing ground is an ‘open’ in the PNK wire between the O2 sensor's engine wiring harness connector and the PCM (since your Corolla's PCM is the one that provides this ground to the O2 sensor's heater element).

TEST 3: Testing The Heater Element's Resistance

Testing The Heater Element's Resistance. Front Oxygen Sensor Heater Test -P0135 (1998-2002 1.8L Toyota Corolla)

OK, now that you've checked the basics (power and ground) we're gonna' check the O2 sensor's heater element's resistance and see if it's within specification.

If your test shows that the O2 sensor's heater's resistance IS NOT within specification, then we can conclude that the upstream sensor is fried and the cause of the P0135: Heated Oxygen Sensor Circuit (Sensor #1) trouble code lighting up the check engine light.

NOTE: Just a reminder that the upstream oxygen sensor has to be completely cold before proceeding with this test since the manual calls for the O2 sensor to be at room temperature for the resistance test.

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).

  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 11 to 16 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: The O2 heater's resistance is within factory specification- This test result tells you that the HO2S 11's heater is OK.

CASE 2: Your multimeter showed an open circuit (OL)- This confirms that the HO2S 11's heater element is fried. Replacing the HO2S 11 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 upstream O2 sensor's heater element is getting power (TEST 1).
  2.      -AND-
  3. Confirmed that the upstream O2 sensor's heater element is getting ground (TEST 2).
  4.      -AND-
  5. In this test you have confirmed that the heater element's resistance is out of specification.

... You can correctly conclude that your 1.8L Toyota Corolla upstream O2 sensor needs to be replaced with a new one.