TEST 2: Checking the O2 Bank 1 Sensor 1 Heater Ground
So far, you've checked and confirmed that the upstream oxygen (O2) sensor, on your Honda Accord, is being fed with plenty of voltage (10 to 12 Volts DC).
The next step, is to check and confirm that the heater element is getting ground... since without this ground, the upstream O2 sensor's heater element won't activate.
NOTE: This ground is provided internally by your Honda Accord's Fuel Injection Computer... so be careful and don't accidentally or intentionally apply 12 Volts to this wire or you'll fry the Fuel Injection Computer.
This is what you'll need to do:
- Disconnect the Front oxygen sensor from its connector (if it isn't already from TEST 1).
- Locate the Orange w/ Black stripe wire (1994-1997 Accord) or the Black w/ White stripe wire (1998-2002 Accord).
- NOTE: You'll test the wire that is on the engine wiring harness connector side and NOT on the O2 sensor itself.
- Place your multimeter in Volts DC mode and:
- Connect the red multimeter lead to battery (+).
- Connect the Black lead to the Orange w/ Black stripe wire (1994-1997 Accord) or the Black w/ White stripe wire (1998-2002 Accord) of the engine wiring harness connector side.
- 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 tells you that the ground circuit is OK.
Now for the final test to determine if the upstream O2 sensor's heater element is fried (internally) on your Honda Accord. Go to TEST 3.
CASE 2: The multimeter DID NOT register 10 to 12 Volts DC- Double-check that you're testing the correct oxygen sensor wire...
... if your multimeter still does not indicate the 10 to 12 Volts DC, then the most probable cause of this missing ground is an ‘open’ somewhere in the wire between the O2 sensor connector and your Honda Accord's Fuel Injection Computer.
Repairing the cause of this missing ground will solve the P0135 trouble code on your Honda Accord.
OK, this is the P0135 Bank 1 Sensor 1 O2 Sensor trouble code test you signed up for! In this section, you're gonna' measure the resistance of the heater element itself (that's inside the upstream O2 sensor) with your multimeter in Ohms (Ω) mode.
The internal heater element, of your Honda Accord's upstream O2 sensor, has to have a resistance between 10 to 40 Ohms. Usually, when the heater element fails, you'll see your multimeter register an infinite resistance, which it usually translates with the letters OL (Over Limit).
OK, this is what you need to do:
- Disconnect your Honda Accord's upstream oxygen sensor from the engine wiring harness connector (if it isn't already from the previous tests).
- NOTE: Your Accord's Front O2 sensor must be disconnected from the vehicle's connector for this test!
- Using the photo in the image viewer... locate the number 3 and number 4 terminals of the oxygen sensor connector.
- With your multimeter in Ohms mode... probe the terminals that correspond to the numbers 3 and 4 of the O2 sensor connector.
- NOTE: remember, you're testing the oxygen sensor itself.
- If all is OK, you should see about 10 to 40 Ω (Ohms).
- 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 confirms that the pre-catalytic converter O2 sensor's heater element on your Honda Accord is OK.
Now, since you have a P0135 lighting up your check engine light, I suggest that you erase the trouble code and road test your Honda Accord.
If the diagnostic trouble code does come back... there are several possible scenarios:
- Intermittent short in the O2 sensor's wiring (that only presents itself when the vehicle is in motion).
- A BAD O2 sensor (even tho' it tested OK in this test section).
- A BAD Fuel Injection Computer (this is rare, but it does happen).
Although it's beyond the scope of this tutorial to test for the above conditions... my suggestion to you, before replacing the Fuel Injection Computer, is to try another O2 sensor first and go from there.
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.
Replacing the oxygen sensor with a new one will solve the P0135 diagnostic trouble code that is illuminating the check engine light on your 2.2L (2.3L) Honda Accord.
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