Front Oxygen Sensor Heater Tests -P0135 (1995-1996 2.0L Neon)

This tutorial will help you to diagnose trouble code P0135 on your 1995, 1996 Dodge (or Plymouth) Neon with either a 2.0L SOHC (Single Over Head Camshaft) or a 2.0L (Double Over Head Camshaft) engine.

When a trouble code P0135: O2 Bank 1 Sensor 1 Heater Circuit Performance lights up the check engine light (CEL) on your Neon's instrument cluster, it's telling you that the oxygen (O2) sensor has a problem with its internal heater and this tutorial will help you to get to the bottom of it.

This upstream oxygen sensor tutorial covers the 1995 and 1996 Dodge Neon (Plymouth Neon) with a 2.0L SOHC or DOHC engine. You can find the 1997, 1998, and 1999 tutorial here: Trouble Code: P0135 Test 2.0L Dodge Neon (1997-1999).

If you need to test the rear 1995-1996 Neon O2 sensor's heater, go here: Rear O2 Sensor Heater Test -P0141 (1995-1996 2.0L Neon).

En Español You can find this tutorial in Spanish here: Pruebas Del Calentador Del Sensor De Oxígeno Delantero -P0135 (1995-1996 2.0L Neon) (at: autotecnico-online.com).

Circuit Descriptions Of The Upstream Oxygen Sensor

Circuit Descriptions Of The Upstream Oxygen Sensor. Front Oxygen Sensor Heater Tests -P0135 (1995-1996 2.0L Neon)

The upstream oxygen sensor, on your Dodge or Plymouth Neon, is known by several different names like O2 sensor before the catalytic converter, or front oxygen (O2) sensor, or Bank 1 Sensor 1, or pre-catalytic converter oxygen (O2) sensor.

Regardless of what it's called, you can count on one thing and this is that the Bank 1 Sensor 1 oxygen sensor has 4 wires sticking out of it.

Knowing what wire does what is key to testing trouble code P0135 and in this section I'll go into some detail on each wire's job description.

Now, we don't have to test all 4 circuits (wires). We only have to worry about 2 of them and these are the ones that supply the heater element with power and Ground.

The chart below will help us to identify all of the upstream oxygen sensor wires on your 95 or 96 Neon with a 2.0L engine (SOHC or DOHC).

O2 Bank 1 Sensor 1 Circuits
Pin Wire Color Description
1 Black w/ Light Blue stripe HO2S Low Signal
2 Black w/ Dark Green stripe HO2S High Signal
3 Black Heater Element Ground
4 Dark Green w/ Orange stripe Heater Element 12 Volts (from Auto Shutdown Relay)

TEST 1: Checking Bank 1 Sensor 1 Power Circuit

Making Sure The Front O2 Heater Is Getting Power. Front Oxygen Sensor Heater Tests -P0135 (1995-1996 2.0L Neon)

The very first thing we'll do is to make sure that the upstream oxygen sensor's heater element is getting 10 to 12 Volts.

This battery power is provided by terminal number 4 of the O2 sensor's harness connector. We'll check for this battery power (voltage) with the Key On Engine Off (KOEO).

IMPORTANT: All of the O2 sensor tests, on your 1995, 1996 Dodge (Plymouth) Neon need to be done with a completely cold engine or you run the risk of getting severely burned by the O2 sensor! Be careful and take all necessary safety precaution!

OK, this is what you'll need to do:

  1. 1

    Locate the upstream oxygen sensor and disconnect it from its electrical connector.

  2. 2

    Locate the wire that connects to the terminal number 4 of the upstream O2 sensor's harness connector (the harness connector is the connector on the engine wiring harness).

    This is usually a dark green with orange stripe (DK GRN/ORG) wire.

  3. 3

    Place your multimeter in Volts DC mode

  4. 4

    With the red multimeter test lead, probe the wire that connects to terminal number 4 of the engine wiring harness O2 sensor connector.

  5. 5

    Ground the black multimeter test lead on the battery negative (-) post.

  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: Your multimeter recorded 10 to 12 Volts DC. This is good and let's you know that the oxygen sensor before the catalytic converter on your Dodge Neon (or Plymouth Neon) is getting power from the Auto Shut Down (ASD) relay.

The next step is to make sure that the oxygen sensor's heater element is getting Ground on terminal number 3 of the O2 harness connector. For this test, go to: TEST 2: Checking The Heater Ground.

CASE 2: Your multimeter DID NOT record the indicated voltage. Re-check that you're testing the correct wire and that the key is in the RUN position (but don't crank or start the engine) and re-test.

If you still don't see 10 to 12 Volts DC then this test result exonerates the upstream oxygen (O2) sensor on your Dodge Neon (Plymouth Neon) as BAD.

Although it's beyond the scope of this article, the next step is to check the continuity of the dark green with orange stripe (DK GRN/ORG) wire between the Bank 1 Sensor 1 oxygen sensor connector and the Auto Shutdown (ASD) relay.