How to Replace an O2 Sensor in a Toyota 4Runner

by Jody L. Campbell

The Toyota 4Runner has at least two oxygen sensors. The newer ones may have up to four. Figuring out which one needs to be replaced may be more difficult than crawling underneath and replacing the sensor. Oxygen sensors were incorporated into the exhaust systems to monitor the amount of oxygen in the burning fuel. A high or lean variance during the operation of the 4Runner can lead to a diagnostic trouble code reported by one or more of the sensors to the computer of the SUV and trigger a "check engine" warning light on the dashboard instrument panel.

Step 1

Drive the Toyota 4Runner up onto the car ramps carefully on a flat surface. Apply the parking brake. Place a wheel chock behind one of the rear tires.

Step 2

Grab all of your tools, put on the safety glasses, and crawl under the Toyota 4Runner on a creeper. Locate the sensor you need to replace. These sensors are bolted into the exhaust system on 4Runners. They are located up high on the front exhaust pipe near the manifold and downstream on the exhaust system near the catalytic converter.

Step 3

Remove the two nuts on the flange of the oxygen sensor you're replacing. It's not uncommon on the 4Runners for these nuts to be severely corroded and will no longer be able to remove with a socket. An extractor socket pounded on with a hammer or a pair of vise grip pliers squeezed against the nut to break it loose enough to un-thread it by hand is usually all it takes.

Step 4

Follow the oxygen sensor wire to the plug connection. It'll be about 7 inches away from the sensor. Unplug the connection by pressing in on the clip lock with a flathead screwdriver and separate the plug. Remove the old sensor and remove the old gasket from the oxygen sensor flange on the exhaust pipe.

Step 5

Clean the threads of each stud using an 8x1.25 millimeter re-threader or die. Install the new gasket onto the flange and place the new oxygen sensor into the porthole. Place the lock washers and nuts onto the studs of the flange and tighten with a ratchet and a socket.

Step 6

Plug the oxygen sensor wire back into the plug connection.

Step 7

Gather up all the tools and crawl out from under the 4Runner. Remove the wheel chock, release the parking brake and lower the 4Runner off of the ramps.

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