This tutorial will help you diagnose a P0135 diagnostic trouble code on your 1994-2002 Honda Accord with either a 2.2L or 2.3L 4 cylinder engine.
A P0135: O2 Bank 1 Sensor 1 Heater Circuit Performance trouble code usually means that the upstream oxygen sensor's heater element is fried and that the oxygen sensor needs to be replaced.
In this tutorial, I'll help you test it and make sure that the upstream O2 sensor is bad or not.
Circuit Descriptions Of The Upstream Oxygen Sensors
By now, I'm sure you've seen/read all of the names that the Bank 1 Sensor 1 Oxygen Sensor goes by. All of the following refer to the same sensor you're gonna' test:
- Oxygen sensor before the catalytic converter.
- Pre-catalytic converter oxygen (O2) sensor.
- Front oxygen (O2) sensor.
- Upstream oxygen sensor (probably the most common name).
To get to the bottom of the P0135 trouble code that's lighting up the check engine light on your Honda Accord, what you and I really need to know (about the upstream O2 sensor) is which circuits (wires) are the ones that feed the internal heater element with power and Ground.
The following chart will help us figure out what wire does what and which 2 of the 4 we need to test.
|O2 Bank 1 Sensor 1 Circuits|
|1||*||HO2S Low Signal|
|2||*||HO2S High Signal|
|3 <-->||Yellow w/ Black stripe||Heater Element Power (1994, 1995, 1996, 1997)|
|3 <-->||Black w/ Yellow stripe||Heater Element Power (1998, 1999, 2000, 2001, 2002)|
|4 <-->||Orange w/ Black stripe||Heater Element Ground (1994, 1995, 1996, 1997)|
|4 <-->||Black w/ White stripe||Heater Element Ground (1998, 1999, 2000, 2001, 2002)|
* Will vary depending on the year of your Honda Accord.
TEST 1: Checking Bank 1 Sensor 1 Power Circuit
To get this show on the road, the first thing you need to do, is make sure that the upstream oxygen sensor's heater element is getting power on your Honda Accord.
You'll check for this power with the Key On Engine Off. This power will be in the form of 10 to 12 Volts as checked by a multimeter.
IMPORTANT: All of the O2 sensor tests, on your Honda Accord, have to be done with a completely cold engine or you run the risk of severe burns! Why? Well, with the engine running, the upstream oxygen sensor absorbs all of the exhaust gas' heat and it gets VERY HOT!
If the engine in your Honda Accord has been running for any length of time, let the engine cool down completely before attempting the tests in this tutorial.
OK, this is what you'll need to do:
- Locate the upstream oxygen sensor and disconnect it from its electrical connector.
- Locate the yellow w/ black stripe wire (1994-1997 Accord) or the black w/ yellow stripe wire (1998-2002 Accord) of the engine wiring harness oxygen sensor connector.
- NOTE: You'll be testing the wire that is on the engine wiring harness connector side (for the upstream O2 sensor) AND NOT the wire on the oxygen sensor side.
- With your multimeter in Volts DC mode:
- With the red multimeter test lead, probe the yellow w/ black stripe wire (1994-1997 Accord) or the black w/ yellow stripe wire (1998-2002 Accord) of the engine wiring harness connector.
- Ground the black multimeter test lead.
- 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: Your multimeter recorded 10 to 12 Volts DC. So far so good, since this is the test result we need to see, and it confirms that the pre-catalytic converter oxygen sensor's heater element is getting power.
The next step is to make sure that your 2.2L (2.3L) Honda Accord's oxygen sensor's heater element is getting a good Ground on the C circuit wire. For this test, go to: TEST 2.
CASE 2: Your multimeter DID NOT record the indicated voltage. Double-check that you're testing the right wire and repeat the test.
If you still don't see 10 to 12 Volts DC, then this test result tells you that the reason the P0135 trouble code is lighting up the check engine on your Honda Accord is a lack of voltage to the upstream O2 sensor's heater element.
The most likely cause will be that the oxygen sensor fuse is blown and needs to be replaced.