The first sign of a problem with a vehicle's oxygen sensor is usually when the “check engine light” comes on. Faulty sensors lead to jerky movements, starting problems, and poor fuel economy if not replaced. These elements are necessary for a vehicle to combine the proper ratio of gas and oxygen in the fuel. Depending on the make and model, you may need to replace 2-4 in your vehicle. Even if you have minimal automotive experience, the sensors are not that difficult to replace. You must turn off the old sensors, install the new ones and then you can appreciate the best performance of the vehicle.
Part 1 of 3: Detect the Error and Secure the Vehicle
Step 1. Use an OBD scanner to detect the faulty sensor
An OBD scanner is a device that plugs into a port on the car's instrument panel and retrieves an error code from the on-board computer, showing you why the check engine light came on. Each error code corresponds to a different part of the vehicle. To detect the responsible sensor, you can record the code in an internet database such as
You can get a scanner online or at most auto parts stores. If you don't have one, you can take the vehicle to an auto parts store or mechanic to find the error code
Step 2. Allow the engine to cool before attempting to remove a sensor
The sensors are located along the exhaust system, which gets too hot when the vehicle is in use. For example, it is dangerous to touch the engine. Turn off the vehicle and wait about 30 minutes for it to cool down. If you need to touch a component before you are sure it is cold, you should wear protective gear.
Look for a heat resistant glove (for example, a welder's glove). In addition, you should wear long-sleeved clothing and safety glasses for additional protection
Step 3. Raise the vehicle if you need to reach a sensor below it
Park the car on a hard, flat surface. Put chocks behind the wheels to keep them from rolling. Next, slide a jack under one of the vehicle's support points. After raising it, you should put a jack stand there to keep the car elevated.
- Starting in 1994 and 1995, manufacturers began to produce vehicles with 2 oxygen sensors. The second sensor can only be accessed by crawling under the vehicle.
- It is dangerous to lift a car, so make sure it is stable before looking for the sensor. If you are not comfortable working under a car, you can enlist the help of a mechanic.
Part 2 of 3: Remove the old sensor
Step 1. Locate the oxygen sensor under the hood or vehicle
Look for a piece that looks like a spark plug with a thick black wire coming out of it. The first sensor will always be located next to the engine in its compartment. It will be found on the exhaust pipe leading from the engine to the rear of the vehicle. Today most cars also have a second sensor behind the catalytic converter, which looks like a metal cylinder above the exhaust duct and is located just behind the front wheels.
Most vehicles built after 2000 actually have 4 sensors. Each vehicle has 2 sensors near the engine and 2 near the catalytic converter
Step 2. Disconnect the electrical connection to the oxygen sensor
Follow the wire away from the end of the sensor connected to the exhaust duct, which will end in a plastic plug inserted into a socket. To remove it, you must locate the small tab over the end of the plug. While pressing down on the tab, you should pull the plug back with your hand.
- If you are having difficulty unplugging the sensor cable, you should push the tab down with a flat screwdriver while pulling the connection with your free hand.
- Avoid trying to cut and then solder the wires to the new oxygen sensor. With the latest sensors, soldering causes the wires to stop working properly.
Step 3. Spray some penetrating oil on the sensor to loosen it
Worn sensors can be difficult to remove, but a good penetrating oil helps to ensure that they come off. Add the lubricant to the opening where the sensor connects to the exhaust duct. You should wait about 10 minutes for the oil to absorb before trying to unscrew the sensor. You may need to apply the oil several times before you can remove the sensor.
Another way to treat a difficult oxygen sensor is to heat its base and threads. Use a heat gun instead of a blowtorch to slightly heat the sensor until you can remove it. A hot air gun does not have a flamethrower, so it is safer than a blowtorch, but you must be careful and protect yourself with the proper safety gear
Step 4. Unscrew the oxygen sensor with a ratchet wrench
The easiest way to disconnect the sensor is by using a 3/8 inch ratchet wrench with a 7/8 inch oxygen sensor wrench. If you don't have these items, you can try using a wrench. Place the key over the sensor where it connects to the exhaust duct. Twist it counterclockwise to loosen, then finish unscrewing by hand.
- All the tools you need are available online or at most auto parts stores. Also, you can check to see if local auto parts stores have a tool rental program.
- If the sensor feels stuck in place, you should avoid forcing it. Apply more penetrating oil as needed to avoid damaging the vehicle. If it is too difficult to remove, you should let a professional take care of it.
Part 3 of 3: Install the New Sensor
Step 1. Choose a new oxygen sensor that is identical to the old one
Take into account the make and model of the car to get the correct sensor. For example, you need to search for a Toyota Prius to get the exact sensor used in a new Prius. Make sure the new sensor is the same size and shape as the old one. Also, it must be from the same brand.
- You can get generic sensors at a cheaper price, but it's best to avoid them for the sake of your vehicle. The only sensor model that works with the vehicle's on-board computer is the same one used by the manufacturer.
- If possible, contact an auto parts store before trying to change the sensor. You can also take the old sensor with you to a store if possible.
Step 2. Add a small amount of release agent to the new sensor
New sensors come packaged with a bronze gel bag. You may be wondering at first what that foreign substance is, but it is a very important lubricant. Open the bag, and then use a clean cloth or glove to spread a small amount of lubricant over the threads of the new sensor. The threads are the grooves in the metal ring near the tip of the sensor.
- To avoid problems with the non-stick, you should use a glove when applying it by hand. If it falls on your skin, it probably won't hurt you, but you should wash your hands thoroughly afterward.
- You don't need too much gel. As long as you apply a little over the thread grooves, the sensor will fit properly into the exhaust duct.
Step 3. Twist the sensor clockwise to secure it over the exhaust duct
Fit the tip of the sensor into the hole in the exhaust duct. Make sure it is centered and enters smoothly as you begin to rotate it clockwise with your hand. Once it's firmly in place, use an oxygen sensor wrench or wrench for a final twist.
You don't need to over-adjust the new sensor. In fact, over tightening it could cause the threads to loosen, making the sensor impossible to remove
Step 4. Plug the electrical connector back into the vehicle
Modern oxygen sensors come equipped with a power cord attached, so you don't need to do any extra work. The cable will hang from the free end of the sensor. Connect it to the socket near the exhaust duct.
Push the plug in until it clicks into place. Make sure the cable does not touch the motor or other parts that get hot when the vehicle is in use
Step 5. Start the car to see if the problem is fixed
The new sensor makes a big difference as it improves fuel economy. Plus, it makes the car sound and run better, and it consumes less fuel. If the check engine light is on, it will most likely go out as well. You can take the car out on the road to make sure it stays off.
- On some vehicles, you may have to turn off the check engine light by hand. Turn off the engine and then start the car with the ignition key. Use the delete function on an OBD scanner to reset the light.
- Disconnect the battery or take the vehicle to a mechanic for additional methods of turning off the check engine light.
- If the check engine light comes back on, then the oxygen sensor was not installed correctly or your vehicle has another problem.
- To determine if a faulty sensor is causing the check engine light to come on, you need to use an OBD2 scanner, which connects to the car and retrieves error codes from the on-board computer to detect the problem.
- Most auto parts stores have code readers that you can borrow to detect a faulty sensor. Employees can even help you use them, but they will also try to sell you replacement sensors.
- To keep the car running smoothly, you need to replace all the sensors at once. If one fails, the others will likely fail soon too, so try to keep the same maintenance schedule.
- You should replace the oxygen sensors approximately every 160,000 km (100,000 miles) on vehicles built after 2000. If you have an older vehicle, you should replace them every 97,000 km (60,000 miles) or sooner.
- You should always let the engine and exhaust system cool down before starting work to avoid accidental burns.
- Crawling under a car is dangerous, so you should prioritize safety and use jack stands.