How To Test Trouble Code P0135 (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.

ES 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).

APPLIES TO: This tutorial applies to the following vehicles:

• 1.7L Honda Civic (DX, EX, LX): 2001, 2002, 2003.

Circuit Descriptions Of The Upstream Oxygen Sensors

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

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 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.

TEST 2: Verifying The Heater Element Is Getting Ground

The BLK/WHT wire, of the upstream O2 sensor harness connector, is the one that supplies the heater element with Ground.

To test this Ground circuit, we'll do a simple multimeter voltage test.

IMPORTANT: The Ground supplied by the BLK/WHT wire is provided directly by your Honda Civic's PCM. Be careful and don't accidentally or intentionally short this wire to battery power, or you'll fry the PCM.

These are the test steps:

1. 1

   Locate the BLK/WHT wire of the O2 sensor's 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:

   1. Connect the red multimeter test lead to battery (+).
   2. Probe the BLK/WHT 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 registered 10 to 12 Volts DC. This test result lets you know that your 1.7L Honda Civic's upstream oxygen sensor's heater element is getting Ground.

So far you've confirmed that the upstream O2 sensor's heater element is getting both power and Ground. The next step is to check the heater element's resistance with your multimeter...for this test, go to: TEST 3: Testing The Heater Element's Resistance.

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 terminal.

If your multimeter still doesn't register the 10 to 12 Volts DC, then the most likely cause of this missing Ground is an 'open' in the BLK/WHT wire between your Honda Civic's PCM harness connector and the O2 sensor's harness connector.

TEST 3: Testing The Heater Element's Resistance

Since you have checked and confirmed that the upstream oxygen sensor on your Honda Civic is getting both juice and Ground, the next (and last) step is to check the heater's internal resistance.

This is another multimeter test but with it in Ohms (Ω) mode and it applies to both the D17A1 and D17A2 upstream oxygen sensor.

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 3 and number 4 of the O2 sensor connector itself (not the engine wiring harness O2 connector).

2. 2

   With your multimeter in Ohms mode, probe terminals number 3 and number 4 of the O2 sensor itself.
   
   NOTE: The upstream O2 sensor for the D17A2 engine has female metal terminals. Avoid probing the front of these female terminals with the multimeter test leads or you run the risk of damaging them.

3. 3

   If all is OK, you should see about 3 to 3.6 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: Your multimeter confirmed the indicated resistance. This test result tells you that your 1.7L Honda Civic's 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. Replacing the upstream O2 sensor with a new one will solve the P0135 trouble code lighting up the check engine light (CEL).

Here are some more specifics: Since you have:

• Confirmed that the upstream O2 sensor's heater element is getting power (TEST 1).
•      -AND-
• Confirmed that the upstream O2 sensor's heater element is getting Ground (TEST 2).
•      -AND-
• In this test you have confirmed that the heater element's resistance is out of specification.

... You can correctly conclude that the upstream O2 sensor on your 1.7L Honda Civic needs to be replaced with a new one.

Location Of The Engine ID

The 1.7L Honda Civic comes in two flavors: D17A1 or D17A2. You can easily identify which engine your Honda Civic has by checking its identification code located on the front of the engine.

The arrow in the photo (above) points to the location of the engine ID number.

Where To Buy The Oxygen Sensor And Save

The one thing to keep in mind, when buying the upstream O2 sensor on your 1.7L Honda Civic, is the fact that the O2 sensor's connector may have male or female terminals.

For the most part, the D17A1 engine uses an upstream O2 sensor that has male terminals in its connector and the D17A2 engine uses an upstream O2 sensor that has female terminals in its connector.

If you find, after testing the upstream oxygen sensor that its heater element is fried, take a look at the links below. I think they'll save you some bucks:

D17A2 Engines:

D17A1 Engines:

NOTE: If you're not sure if the above upstream O2 sensor fit your particular 1.7L Honda Civic, don't worry, once you get to the site, they'll make sure the sensor is the right one, if not, they'll find you the right one.

More 1.7L Honda Civic Diagnostic Tutorials

You can find a complete list of diagnostics tutorials for your 1.7L Honda Civic in this index:

• 1.7L Honda Civic Index Of Articles.

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

• How To Test The MAP Sensor (2001-2005 1.7L Honda Civic).
• How To Test For A Blown Head Gasket (2001-2005 1.7L Honda Civic).
• How To Test The Crank Sensor (2001-2005 1.7L Honda Civic).
• How To Test Trouble Code P0141 (2001-2005 1.7L Honda Civic).