There are several common symptoms of a bad air/fuel sensor, the main one being a check engine light. Read this post for information on how to fix this common problem for a v6 2002-2003 Lexus es300 or Toyota Camry v6 3.0L.

Air/Fuel Sensor

The oxygen sensors (sometimes also called oxygen, o2, or lambda sensors) located in the exhaust stream of the engine help regulate the amount of air and fuel flowing through the system.

Unfortunately, it is common for these sensors to fail in Toyota/Lexus vehicles with the 3.0L engine in the years 2002-2003.

Old Air/Fuel Sensor Removed from a 2002 Lexus ES300

Common Problem for Toyota/Lexus Vehicles

The most common problem you will see with this, is a check engine light (CEL). When you read the error codes using a code-reader, you will see either p1155 or p1135, or both. Sometimes other codes may show up as well.

P1135 – Air/Fuel sensor heater circuit malfunction (Bank 1 Sensor 1)

P1155 – Air/Fuel sensor heater circuit malfunction (Bank 2, Sensor 1)

If you see error code p1155, consider yourself lucky because this is the o2 sensor that is easy to reach (Bank 2)! It can be access from under the hood near the front of the engine.

If you see error code p1135, you will need to jack up the car and get under it.

Replacement Parts

For this repair, you will need the following tools and supplies:

Editor's Note: For many parts, 3rd party suppliers are sufficient, but in the case of Air/Fuel sensors, it is highly recommended that you go with the OEM supplier for Toyota, which is Denso. Do not think you will save money buying a cheaper part in this case. You will not fix it, and you will only have more mechanics bills. Read the reviews on Amazon.com to hear this familiar story over and over again. 
Note: the same sensor is used for both B1S2 and B2S2.

Tools Needed

How to Replace the Air/Fuel Sensor – Step by Step

In my case, I had the error code P1135 as read from my OBD2 reader, so I ordered the Denso 234-9047 Air/Fuel Sensor and an Oxygen Sensor socket, then jacked up the front of my 2002 Lexus es300 v6 (which is very similar to the 2002-2003 Camry)

Then, locate the defective sensor. From under the car, the sensor is against the firewall, sticking out of the exhaust flange. Refer to the picture below, where the front of the car is up.

Location of the Air/Fuel Sensor

Next, spray the sensor threads with some penetrating oil and let it soak for at least 15 minutes. If you can spray this on several days ahead, that may help as well.

PB Blaster sprayed on the sensor threads

Make sure you have an o2 sensor socket. These have a slot to accommodate the wire. Also, a wrench will not fit down into the slot created by the heat baffle.

Oxygen Sensor Socket

Position the Oxygen Sensor Socket onto the A/F sensor for removal.

Turn the sensor counterclockwise to remove it. It will likely be very, very tight.

Hint: If the A/F sensor will not come loose, start the car and let it idle for about 5 minutes then shut it off. The heat will expand the collar, making the removal easier. (Be careful however, the exhaust components will be hot!)

Once the A/F sensor is loose, use a flat-bladed screwdriver to pry the electrical connection tab out, away from the sensor plug.

Press the tab outward
Use a screwdriver to pry the tab outward
Hint: Space is limited, so using a short-handled screwdriver may be easier. You can jam it into the opening, and with the same hand, pull the plug out.

Unscrew the A/F sensor the rest of the way and remove it from the vehicle.

Next, put some anti-seize onto the threads of the new A/F Sensor.

Apply anti-seize to the threads

Then put it into the port and tighten it up with the O2 Socket.

Install the new O2 sensor
Note: Don't overtighten it! Air/Fuel sensors are commonly torqued to 31 ft-lbs.

Once the new sensor is in, plug in the electrical connector by lining up the tabs and pressing it into the connector until you hear a click.

That’s it! Check engine light can be reset if you have an OBD2 reader, otherwise, the light will go out after several miles of driving.

I hope you found this guide helpful!

Replacement Parts

For this repair, you will need the following tools and supplies:

Note: the same sensor is used for both B1S2 and B2S2.

Tools Needed