The P0135 Honda trouble code means that your primary oxygen sensor heater circuit is not performing the way your ECU expects it. Because of this heater circuit malfunction, your Powertrain Control Module (PCM) may not receive all the information it requires to operate your engine in closed loop mode.
Closed loop is the mode in which your vehicle’s PCM will always try to adjust itself to. Your Honda ECU is constantly trying to reach a
If you’ve got this check engine light illuminated on your dash, it’s time to take a look at our How To Test a 02 Sensor for 2.2L Honda engines. Because your heater element is not properly powering your primary oxygen sensor, the readings being provided to the PCM can be inaccurate or may not exist at all.
Today I’ll be showing you how to test, resolve and repair the P0135 Honda OBDII trouble code in your 1994-2001 Honda Accord 4 cylinder engine, with either a 2.2L (F22) or 2.3L (F23) engine. The vehicle I’ll be working on is a 1999 Honda Accord 4 cylinder 2.3L VTEC F23, but the testing procedure applies to any SOHC 2.2 or 2.3L Honda engine.
Common causes of the
P0135 Honda Check Engine Light
- Bad upstream oxygen sensor
- Break in 02 sensor heater wires
- Low power or bad battery / alternator
What does the Upstream 02 sensor do?
As stated at the beginning of our How To Test a 02 Sensor article, the upstream or primary oxygen sensor enables the PCM to control fuel curves real time for maximum efficiency. This mode is commonly referred to as closed loop operation, and is vital to your vehicle’s fuel economy.
Where is the upstream 02 sensor located?
The upstream or primary 02
How To Test a 02 Sensor – Honda 2.2L
Now that you know where the primary oxygen sensor is located, you can trace back the wiring harness and locate the clip you need to disconnect. The primary 02 sensor connector is secured to a transmission bracket, and you’ve got to push up on this pin to release the connector itself.
With the oxygen sensor now disconnected, you will be using your voltmeter or multimeter to read PIN 3 and PIN 4, which represent the heater wires on your 02
Because these two lower pins are strictly the oxygen sensor heater element wires, you will be testing these directly for lack of power. Lack of power from your Honda or the dreaded check engine light for
P0135 Honda
For our 1999 Honda Accord, the colors and pinout reading for the upstream 02
- PIN 1 – H02S Low Signal
- PIN 2 – H02S High Signal
- PIN 3 – Heater Element – Black wire with yellow stripe ( for 1998, 1999, 2000, 2001 Honda Accord )
- PIN 4 – Heater Element – White wire with red stripe ( for 1998, 1999, 2000, 2001 Honda Accord )
Now take your voltmeter or voltage reading device and connect the black wire to your battery negative terminal to provide ground. Place the red lead of your multimeter to PIN 3 which is the black wire with yellow stripe for the 1998-2001 Honda Accord.
With the key set to the “ON” position but the engine is not running, you should see 12 volts of power signal here at this pin. If you do have 10-12 volts here at this pin, move onto PIN 4 which is the white wire with red stripe. This wire should also be delivering 10-12 volts to your primary oxygen sensor, if you do not have power at either of these wires, or just one you need to replace the upstream oxygen sensor.
The part number for this upstream oxygen sensor is 36531-PAA-307 but for the F23 VTEC engine, you can also find the primary 02 sensor under the following part numbers.
36531-PAA-L21
36531-PAA-L22
36531-PAA-L23
36531-PAA-L41
Did you find this How To Test a 02 Sensor Guide helpful to resolving your P0135 Honda trouble code? Have any questions about this
