P0135 Trouble Code Diagnostic Tests (2001-2003 1.7L Honda Civic)

A P0135: Primary Heated Oxygen Sensor (Primary HO2S)(Sensor 1) Heater Circuit Malfunction trouble code on your 1.7L equipped 2001-2003 Honda Civic indicates that the upstream O2 sensor has a problem with its heater element.

Fortunately, testing the upstream sensor's heater element is pretty easy and in this tutorial I'll show you how in a step-by-step way.

The O2 sensor heater element test I'm gonna' show you doesn't require a scan tool. All you'll need is a multimeter.

En Español You can find this tutorial in Spanish here: Cómo Verificar Código de Sensor de Oxígeno P0135 (2001-2003 Honda 1.7L) (at: autotecnico-online.com).

Circuit Descriptions Of The Upstream Oxygen Sensors

How To Test Trouble Code P0135 (2001-2003 Honda 1.7L) How To Test Trouble Code P0135 (2001-2003 Honda 1.7L)

This tutorial covers the Honda Civic DX, EX, and LX models which are equipped with one of two 1.7L engines. The Honda Civic DX and LX models are equipped with the D17A1 engine and the EX uses the D17A2 engine. Even though the 3 tests apply to both engines... the upstream O2 sensors are a bit different and are not interchangeable.

The difference is in that the upstream O2 sensor for the D17A1 engine has male terminals in its connector and the upstream O2 sensor for the D17A2 engine has female terminals in its connector. So, you'll need to identify what specific 1.7L engine is in your Civic if you need to buy and replace it.

Finding out the engine code isn't hard, since this engine identification number is stamped onto the block itself and is located on a flat square area to the right (passenger side) of the exhaust manifold. You can find the location of the engine ID here: Location Of The Engine ID.

As you're already aware, there are 4 wires coming out the upstream O2 sensor. 2 of these 4 wires provide power and ground to the heater element. The other 2 are the ones that provide the oxygen content info of the exhaust, to the PCM (Powertrain Control Module = Fuel Injection Computer).

Here are the circuit descriptions of the 4 wires (taking into account the engine code):

D17A1 and D17A2 Upstream Oxygen Sensor Pinout
(2001-2003 1.7L Honda Civic)
Pin Wire Color Description
1 GRN/YEL SG2 (Sensor Ground)
2 WHT PHO2S (Sensor Signal)
3 BLK/WHT Heater Element Ground
4 BLK/YEL Heater Element Power

TEST 1: Verifying The Heater Element Is Getting Power

P0135 Trouble Code Diagnostic Tests (2001-2003 1.7L Honda Civic)

The wire that supplies power to the upstream oxygen sensor is the BLK/YEL wire (black w/ yellow stripe) of the upstream O2 sensor harness connector (on both D17A1 and D17A2 engines).

Power, which is in the form of battery voltage, is provided by the #4 10 amp fuse located in the underdash fuse/relay box of your Honda Civic.

IMPORTANT: The O2 sensor can get and stay very hot! Perform this test with a completely cold engine. Be careful and take all necessary safety precautions!

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

  1. 1

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

  2. 2

    Locate the BLK/YEL wire of the engine wiring harness oxygen sensor connector.

  3. 3

    With your multimeter in Volts DC mode, probe the BLK/YEL with the red multimeter test lead.

    Ground the black multimeter test lead directly on the battery's negative terminal.

    NOTE: The D17A1 O2 sensor harness connector has female metal terminals. You should avoid probing the front of these female terminals or you run the risk of damaging them permanently with the multimeter's test lead.

  4. 4

    With the Key On Engine Off (KOEO), 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- So far so good since this test result confirms that the upstream oxygen sensor's heater element is getting power.

The next step is to make check that the BLK/WHT wire, of the O2 sensor harness connector, is feeding ground to the heater element. For this test, go to TEST 2: Verifying The Heater Element Is Getting 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 tells you that the upstream oxygen (O2) sensor itself, on your 1.7L equipped Honda Civic IS NOT BAD since without power, the heater element won't work.

Although it's beyond the scope of this article... the next step is to find out why this battery power is missing using a wiring diagram.