The upstream Accord O2 Sensor in your 2.2 or 2.3 liter Honda is also known as the primary oxygen sensor. When the upstream or front oxygen sensor in your Honda starts to go bad, or becomes fouled it will negatively impact your SOHC F series engine operation. There are several Accord oxygen sensors in your Honda, depending on what engine came in your vehicle.
Today I’ll be showing you how to test the upstream Honda Accord oxygen sensor in a 2001 Honda with the SOHC 2.3 liter engine in it. If your Honda Accord begins to run rough, and you see your check engine light on you’ll need to use a OBDII scan tool to figure out what your trouble code is.
In order to complete this test you’ll need a digital multimeter as well. This device allows you to do two things to test your oxygen sensor.
One it will check for power and ground at your O2 harness. This ensures that your upstream oxygen sensor is getting what it needs to operate the heater element.
Secondly you can test the internal resistance of your upstream oxygen sensor to make sure that it’s still in good shape. If you are testing your Honda Accord oxygen sensor and find that it’s defective, you’ll need to replace it.
Common Honda Accord issues
Some of the more common Accord symptoms from a failed Sensor 1 primary oxygen sensor include :
- Bad gas mileage
- Black smoke from exhaust
- Rough idle
- SOHC VTEC engine runs rich
- Check Engine Light ON
Because your Honda engine computer won’t know how rich or lean your engine is running, chances are your SOHC 2.3 liter engine will run poorly.
If it’s running excessively rich this can lead to your engine oil breaking down prematurely and your catalytic converter failing. Neither one is a desirable condition in your Honda, especially for a ULEV Accord.
The is due to the excessive gas in your air/fuel mixture breaking down your oil. When your oil viscosity breaks down, it won’t protect your engine bearings sufficiently. Left untreated this can lead to you spinning a rod bearing and possibly destroying your 2.2 or 2.3 liter engine.
Where is my primary Honda Accord oxygen sensor?
To begin this guide, you’ll need to open your Honda Accord hood and locate the primary oxygen sensor. This unit is mounted into the exhaust header and can be easily seen by looking down in front of your engine.
This sensor is connected to a four pin weatherproof connector. Simply follow the Accord O2 sensor wiring back until you locate the connector. Depress the locking tab and unplug your front Honda oxygen sensor.
Once you have your primary Honda Accord oxygen sensor disconnected, you can begin our testing guide.
Test your Honda Accord O2 sensor heater element
The heater element in your primary oxygen sensor is easy to test. This test is for the 1995-2002 Honda Accord, but the Accord O2 sensor wire colors will vary depending on your car. The wires you will be testing are on the ENGINE harness side, not the sensor.
Insert your Honda Accord ignition key and turn your ignition to the “ON” position. This 
sends power to your engine sensors. Now you will be referencing our Honda Accord oxygen sensor wiring diagram below to test your heater element.
PIN C on your Honda Accord is the Heater Element power. The Accord O2 sensor wiring diagram below will tell you which wire to check depending on your year Honda.
Heater Element Power
- 1994-1997 Honda Accord PIN C – Yellow wire with a BLACK stripe
- 1998-2002 Honda Accord PIN C – Black wire with a YELLOW stripe
Heater Element Ground
- 1994-1997 Honda Accord PIN D – Orange wire with a BLACK stripe
- 1998-2002 Honda Accord PIN D – Black wire with a WHITE stripe
Measure your Accord O2 sensor internal resistance
If you have power and ground circuits at your oxygen sensor heater element, the next test is to check the resistance of your O2. Take your digital multimeter and turn the dial to read resistance Ω, and then you are ready.
Because you are testing the female spades of your oxygen sensor, you will need to take care. Never force the leads of your multimeter into the female housing of your Accord O2 sensor.
Doing so could cause a permanent contact issue with your primary or upstream oxygen sensor and the harness.
Gently probe PIN C AND D of the oxygen sensor to read the internal resistance. Don’t forget that you are checking the SENSOR side of your Accord oxygen sensor.
If your Honda Accord O2 sensor is still good, you should see between 10 to 40 Ω of resistance. However if your multimeter shows an open condition (OL) or a different resistance value, you must remove your Accord oxygen sensor.
When you’ve found that your Honda upstream oxygen sensor has failed, you must remove it. Install your replacement primary oxygen sensor and then use your OBDII scan tool to erase your Honda Accord check engine light.
Have any questions about this Accord O2 Sensor DIY tutorial? Leave us a comment below and let us know!
