Denso Jeep O2 Oxygen Sensor
What You will Need
• Denso Upstream Oxygen Sensors
• Denso Downstream Oxygen Sensors
• Oxygen Sensor Removal Tool
• Ratchet U-Joint
• Ratchet
• Torque Wrench
• Breaker Bar

Part Numbers

Upstream O2 Sensors:

Downstream O2 Sensors:

Upstream O2 Sensors:

Downstream O2 Sensors:

Upstream O2 Sensors:

Downstream O2 Sensors:

NOTE: All part numbers are for a 99-00 California emissions Jeep with a 4.0L engine. 4x4xplor.com is not responsible for the accuracy of any information contained on this write-up.

Oxygen Sensor Replacement
1999-2000 Jeep Wrangler TJ 4.0L Engine
California Emissions

As a part of routine maintenance, it is important to replace the oxygen sensors on your Jeep TJ once it hits 100,000 mile. Even if your engine seems to be running fine, a new set of oxygen sensors will help provide good fuel economy and restore any lost engine power you weren't even aware was gone in the first place. Unfortunately, each new oxygen sensor can cost about $50-$90 depending on the make and part number. And, to make matters worse, if you live in California or have a Jeep made with California emissions on it, you will need to replace a total of 4 sensors (2 upstream and 2 downstream). If you are in a pinch for cash, just replace the 2 upstream oxygen sensor as they will be the ones causing you the most grief.

Fortunately, installing your new oxygen sensors is easy and should only take you about 10 minutes to do. In other words, do not pay someone to do this for you :)

Removal & Installation
California Jeep 4.0L Upstream O2 Sensors On a California Emissions built Jeep 4.0L engine, the 2 upstream O2 Sensors are located just below the intake manifold and above the 2 mini-cats (catalytic converters). Each sensor has a unique pig tail and part number.
California Jeep 4.0L Downstream O2 Sensors Just below the mini-cats, you will find the 2 downstream O2 sensors. Again, each sensor has a unique part number and different length pigtail. Be sure to make a note of which part number goes to which side.
Denso Jeep O2 Oxygen Sensor I purchased a set of Denso O2 sensors which came complete with the appropriate length/type of pigtail, electrical connector and anti-seize compound.
Oxygen Sensor Removal Tool In order to remove and install you O2 sensors, you will need a special remover tool that looks like this. Basically, it is a large socket with a slit in the side of it to allow the pigtail to extend out of it.
O2 Sensor Pigtail 1. With your engine at an ambient temperature, pop open your hood and disconnect the O2 sensor connected to the wiring harness near the firewall of your Jeep. Be sure to make a note of how this pigtail is routed down to the exhaust.
O2 Sensor Pigtail 2. Now, disconnect the O2 sensor pigtail from the wiring harness close to the front of your engine. Again, make a note of how this pigtail is routed down to the exhaust.
Jeep Upstream O2 Sensor Removal 3. Climb underneath the driver side of your Jeep, and remove just one of your O2 sensors using the removal tool. The O2 sensors are located in a tight area and may be a bit difficult to remove. Using a ratchet U-Joint will make this job easier. Also, it may be necessary to use a breaker bar to free the O2 sensor. DO NOT use any lubricants or penetrating oils to assist you in this task.
Denso O2 Sensor 4. Go to your work bench, open up the Denso Oxygen Sensor that matches the part number or has the same pigtail as the O2 sensor you just removed. Then, apply a some of the anti-seize compound that came with the O2 sensor to the threads of it. NOTE: O2 sensors are very delicate so make sure to handle it carefully.
Jeep Upstream O2 Sensor Installation 5. Back underneath your Jeep, carefully thread the O2 sensor into its port by hand. Once all the way on, tighten the O2 sensor to 22 ft. lbs. of torque (30 N-m). If you find it's very difficult to thread in by hand, DO NOT force it in as it may cross the threads and damage them. Instead, use a re-threading tool to clean the threads and try again.
Jeep Upstream O2 Sensors 6. Route the pigtail back up to the top of your engine, climb out from under your Jeep and then plug it in to the wiring harness. Repeat steps 3-5 on all the other sensors.

That should be it. Your are now good for another 100,000 miles before you have to do this all over again. Please let me know if you have any questions.

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