Front O2 Sensor Heater Test -P0135 (1997-1999 2.0L Neon)

TEST 2: Checking The Heater Ground

The other thing that the upstream oxygen sensor's heater element (on your 97, 98, or 99 Neon) needs is Ground.

Without this Ground, the heater (within the pre-catalytic converter O2 sensor) won't activate.

And so, our next testing step, in troubleshooting the P0135, is to make sure that the Bank 1 Sensor 1 oxygen sensor is getting Ground in this wire.

This is what you'll need to do:

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.
   
   You'll test the wire that is on the engine wiring harness connector side and NOT on the O2 sensor itself.

3. 3

   Place your multimeter in Volts DC mode.

4. 4

   Connect the red multimeter test lead to battery positive (+) post.

5. 5

   Connect the black multimeter test lead to terminal number 2 of the O2 sensor's harness connector.
   
   On your Dodge Neon, this should be the black wire of the connector.

6. 6

   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 voltage confirms that the pre-catalytic oxygen sensor is getting Ground.

Now that you know that the upstream O2 sensor (on your 97, 98, or 99 Dodge Neon) is getting fed both power and Ground, the next and final test, is to see if the heater element itself is bad or not. 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 problem, 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 Chrysler vehicle.

TEST 3: O2 Heater Resistance Test

Alright, you've come to the final test. This test will tell you if the internal upstream oxygen (O2) sensor heater is good or bad.

You'll accomplish this test by simply measuring the resistance of the heater element with your multimeter in Ohms (Ω) mode.

If you've reached this point in this tutorial, you have checked and confirmed that:

One: The upstream oxygen (O2) sensor's heater element is getting power (10 to 12 Volts DC) on terminal number 1 of the O2 harness connector TEST 1).

Two: In TEST 2, you confirmed that terminal number 2 is providing Ground for the heater element.

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).

OK, this is what you need to do:

1. 1

   Disconnect the upstream oxygen sensor from the engine wiring harness connector (if it isn't already from the previous tests).
   
   NOTE: The O2 sensor must be disconnected from the vehicle's connector for this test!

2. 2

   Place your multimeter in Ohms mode.

3. 3

   Locate the O2 sensor terminals number 1 and number 2 of the connector with the round male terminals.

4. 4

   Probe terminal number 1 and number 2 with the multimeter test leads.
   
   NOTE: Remember, you're testing the round male terminals of the connector of the oxygen sensor itself.

5. 5

   Your multimeter should give you a reading of about 4 to 7 Ω's.
   
   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.

Every now and then, I've seen it happen where the O2 sensor's heater element is getting both power and Ground, but the P0135 DTC keeps popping up and lighting the check engine light.

When this has happened, it's usually one of two reasons: an intermittent open-circuit problem in the wiring between the Bank 1 Sensor 1 O2 sensor and the PCM or the PCM is bad (although a bad PCM is rare, it does happen).

It's beyond the scope of this tutorial to check for the above two conditions but you at least now know in what direction to take your diagnostic.

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 97, 98, 99 Dodge Neon (Plymouth Neon).

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

More 2.0L Neon Tutorials

You can find a complete list of tutorials for you 2.0L Neon here: Chrysler 2.0L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test The Fuel Injectors (1996-1997 2.0L Neon).
• Rear O2 Sensor Heater Test -P0141 (1995-1996 2.0L Neon).
• 1995-1996 Neon Power Distribution Center.
• How To Test The TP Sensor (1995-2002 Dodge Neon).