Tools You'll Need:
* New O2 sensor: Make sure you get the correct sensor for your vehicle's year, engine, and location (upstream or downstream). The part number should be on the old sensor or can be found in your owner's manual or online auto parts store.
* Wrench or socket: The size will depend on the sensor; often a 7/8" or 1" wrench/socket will be needed. An oxygen sensor socket with a swivel is highly recommended as it will make accessing the sensor much easier. This socket prevents damage to the sensor.
* Penetrating oil (like PB Blaster): This will help loosen a stubborn sensor. Apply generously and let it sit for a while before attempting to remove the sensor.
* Jack and jack stands (highly recommended): Raising the vehicle will provide better access and working conditions.
* Gloves: Protect your hands from grease and potential cuts.
* Rags or shop towels: To clean up any spilled oil or coolant.
* Torque wrench: Essential for tightening the new sensor to the correct specification. Overtightening can damage the sensor or exhaust manifold.
* Wire brush (optional): To clean any corrosion off the sensor threads or the exhaust manifold.
Steps:
1. Safety First: Disconnect the negative battery terminal before starting any work. This prevents electrical shorts. Park on a level surface, engage the parking brake, and use jack stands if you raise the vehicle.
2. Locate the O2 Sensor: The 1999 Jeep Cherokee typically has one or more O2 sensors. One is usually located before the catalytic converter (upstream) and another after (downstream). Consult your repair manual or a diagram to pinpoint the location of the sensor you need to replace. Upstream sensors tend to fail more frequently.
3. Access the Sensor: You'll likely need to get under the vehicle to reach the O2 sensor. This often requires maneuvering around exhaust components and other parts of the undercarriage.
4. Prepare the Sensor for Removal: Spray penetrating oil liberally onto the threads of the old O2 sensor. Let it soak for at least 15-30 minutes to loosen it up.
5. Disconnect the Electrical Connector: Carefully unplug the electrical connector from the old O2 sensor.
6. Remove the O2 Sensor: Use the appropriate wrench or oxygen sensor socket to carefully unscrew the sensor. It may be tight, so apply steady pressure and avoid stripping the threads. If it's really stuck, consider using a longer wrench or breaker bar for more leverage. Rock the sensor back and forth gently while turning to help break it free.
7. Clean the Threads: Use a wire brush to clean any corrosion or debris from the sensor threads and the exhaust manifold.
8. Install the New O2 Sensor: Screw the new O2 sensor into the exhaust manifold by hand initially to ensure it starts straight. Then, carefully tighten it using the wrench or socket, but do not overtighten. Refer to your repair manual for the proper torque specification. Overtightening can damage the sensor and/or the exhaust manifold.
9. Reconnect the Electrical Connector: Carefully plug in the electrical connector to the new O2 sensor.
10. Lower the Vehicle (if applicable): Carefully lower the vehicle using your jack if you raised it.
11. Reconnect the Battery: Reconnect the negative battery terminal.
12. Clear the OBD-II Codes (optional but recommended): After replacing the O2 sensor, you may need to clear any diagnostic trouble codes (DTCs) that have been stored in your vehicle's computer system. Many auto parts stores can do this for free.
Important Considerations:
* Exhaust System Heat: The O2 sensor operates at very high temperatures. Allow the exhaust system to cool completely before working on it to avoid burns.
* Exhaust Leaks: After installation, check for any exhaust leaks around the new sensor.
* Oxygen Sensor Type: There are different types of oxygen sensors (heated or unheated). Make absolutely sure you get the correct replacement sensor for your Jeep.
If you are not comfortable performing this repair yourself, it's best to take your vehicle to a qualified mechanic. Improper installation can damage the sensor or other components. Remember to always consult your repair manual for specific instructions and torque specifications.
