A failed upstream O2 sensor heater element causing a P0135: Primary Heated Oxygen Sensor (Primary HO2S)(Sensor 1) Heater Circuit Malfunction trouble code is a very common problem on the 1.6L Honda Civic.
Thankfully, the upstream O2 sensor's heater element can be easily tested with just a multimeter (no scan tool required) and in this tutorial, you'll find out how.
Contents of this tutorial:
ES 
You can find this tutorial in Spanish here: Cómo Probar El Código P0135 (1995-2000 1.6L Honda Civic) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 1.6L Honda Civic DX: 1995, 1996, 1997, 1998, 1999, 2000.
- 1.6L Honda Civic EX: 1995, 1996, 1997, 1998, 1999, 2000.
- 1.6L Honda Civic LX: 1995, 1996, 1997, 1998, 1999, 2000.
MAP AND TPS SENSOR TESTS:
- How To Test The MAP Sensor (1995-2000 1.6L Honda Civic).
- How To Test The Throttle Position Sensor (1995-2000 1.6L Honda Civic).
Circuit Descriptions Of The Upstream Oxygen Sensors
Your Honda Civic's upstream O2 sensor is a 4-wire sensor.
Each wire has a specific job to do. The two that we're gonna' be concerned about, to diagnose the P0135 trouble code lighting up your Civic's check engine light, are the ones that carry power and Ground to the upstream O2 sensor's heater element.
The table below shows a brief description of the front O2 sensor's circuits:
Here are the circuit descriptions of the 4 wires (taking into account the engine code):
| Upstream Oxygen Sensor Pinout (1995-2000 1.6L Honda Civic DX, EX, and LX) |
||
|---|---|---|
| Pin | Wire Color | Description |
| 1 | WHT | PHO2S (Sensor Signal) |
| 2 | GRN/BLK | SG2 (Sensor Ground) |
| 3 | BLK/YEL | Heater Element Power |
| 4 | BLK/WHT | Heater Element Ground |
Where To Buy The Oxygen Sensor And Save Some $
I remember paying between 60 to 70 bucks for an upstream O2 sensor at my local auto parts store (and thinking I was getting a good deal). Well, I don't anymore.
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:
19%
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NOTE: If you're not sure if the above upstream O2 sensor fit your particular 1.6L Honda Civic, don't worry. Once you get to the site, they'll make sure the O2 sensor is the right one, if not, they'll find you the right one.
TEST 1: Verifying The Heater Element Is Getting Power
To get our P0135 diagnostic off the Ground, the first thing we'll do is check that the BLK/YEL wire (of the harness connector) is feeding power to the upstream O2 sensor's heater element.
This is the first of 3 multimeter tests that we'll do to diagnose the front oxygen sensor on your Honda Civic (DX, EX, or LX).
IMPORTANT: If your Honda Civic's engine has been running, wait till it cools down completely. The O2 sensor can get and stay very hot! Be careful and take all necessary safety precautions!
OK, this is what you'll need to do:
- 1
Disconnect the upstream oxygen sensor from its harness connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Probe the black with yellow stripe (BLK/YEL) wire with the red multimeter test lead.
NOTE: You should avoid probing the front of the harness connector's female terminals or you run the risk of damaging them permanently with the multimeter's test lead. I recommend back probing the connector or using a wiring harness connector. - 4
Ground the black multimeter test lead directly on the battery's negative (-) terminal.
- 5
Turn the key to the ON position but don't crank or start the engine.
- 6
The BLK/YEL 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 voltage test result tells you that the BLK/YEL wire is feeding the upstream oxygen sensor's heater element with 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 re-test.
If you still don't see 10 to 12 Volts DC then you now know that the O2 sensor itself is not causing the P0135 code, since without power the upstream O2 sensor's heater 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
So far, you've confirmed that the YEL/BLK wire is feeding 12 Volts to your 1.6L Honda Civic's upstream O2 sensor.
The next step is to check that the BLK/WHT wire, of the upstream O2 sensor harness connector, is feeding the heater element with Ground.
IMPORTANT: The BLK/WHT wire connects directly to your Honda Civic's PCM, since this Ground is provided by the PCM internally. So 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
Place your multimeter in Volts DC mode.
- 2
Disconnect the front O2 sensor from its electrical connector.
- 3
Connect the red multimeter test lead to battery positive (+) terminal.
- 4
Probe the black with white stripe (BLK/WHT) wire of the O2 sensor's harness connector.
- 5
Turn the key to the ON position but don't crank or start the engine.
- 6
The BLK/WHT 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 1.6L 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
If you've reached this point, you have eliminated a lack of power or Ground as the cause of the P0135 trouble code.
In this last test, you'll check the resistance of the heater element itself with your multimeter in Ohms mode (Ω).
NOTE: The manual calls for the O2 sensor to be at room temperature for the resistance test, so make sure the engine (and the upstream O2 sensor) is completely cold.
OK, this is what you need to do:
- 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
Place your multimeter in Ohms mode.
- 3
Probe terminals number 3 and number 4 of the connector 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. - 4
If all is OK, you should see about 10 to 40 Ω's 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 1.6L Honda Civic's pre-catalytic converter oxygen (O2) sensor's heater is OK.
CASE 2: Your multimeter showed an open-circuit (OL). This resistance test result tells you that the heater element is fried in the upstream O2 sensor and that it needs to be replaced if you have:
- Confirmed that the upstream O2 sensor's heater element is getting power (TEST 1).
- Confirmed that the upstream O2 sensor's heater element is getting Ground (TEST 2).
- 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 1.6L Honda Civic needs to be replaced with a new one and that this will resolve the P0135 trouble code.
More 1.6L Honda Civic Test Tutorials
If this tutorial was helpful/informative, you can find a complete list of 1.6L Honda Civic tutorials in this index:
Here's a sample of the tutorials you'll find there:
- How To Test For A Blown Head Gasket (1995-2000 1.6L Honda Civic).
- How To Test The Alternator (1996-2000 1.6L Honda Civic).
- Testing Shift Control Solenoid Valves A and B (1996-2000 1.6L Honda Civic).
- How To Troubleshoot A No Start (1995-2000 1.6L Honda Civic).
- How To Test The Igniter, Ignition Coil Accord, Civic, CRV, and Odyssey (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!
