Oxygen sensors monitor the exhaust stream, comparing the oxygen content in it to the oxygen content of ambient air. When oxygen content is low, sensor voltage is high. When oxygen content is high, sensor voltage is low. The voltage created by the sensor is sent to the DME (engine control module) to help maintain a proper fuel mixture. The mixture preparation is used to keep the catalytic converters running at peak efficiency. The oxygen sensors used in E60 models covered in this article has four wires. Two of which are for oxygen sensor heating and two for the signal. The heater is used to get the sensor online faster. Previously, exhaust heat was used. One wire supplied a ground to the sensor for the signal, and the other was for the sensor signal.
Oxygen sensors should be replaced every 100,000 miles. In a perfect world that would be it. Wait until a specified mileage and replace the sensor. However, these sensors fail prematurely, set oxygen sensor fault codes and reduce fuel economy. In this article, I will show you how to identify the location of all four oxygen sensors and how to replace them. You will need an oxygen sensor socket to remove the sensors and remember to always work with a cool exhaust. Oxygen sensors are fragile. Do not drop, as damage may occur. Also, keep the sensor tip clean when reinstalling.
Oxygen sensors are laid out in banks, which refer to cylinders and in sensor numbers referring to before or after the catalytic converter. Bank1 or B1 refers to cylinders 1-3. Bank 2 or B2 refers to cylinders 4-6. Sensor 1 or S1 refers to the sensor before the catalytic converter. Sensor 2 or S2 refers to the sensor after the catalytic converter.
Remember that your car may have been serviced before and parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.
Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.
Our vehicle may vary slightly from yours as models do change and evolve as they grow older. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.
Figure 1
Bank 1 Sensor 1 is indicated by a yellow arrow. Bank 2 Sensor 1 is pointed out with a green arrow.
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Figure 2
Bank 1 Sensor 2 has a green arrow. Bank 2 Sensor 2 is shown with a yellow arrow.
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Figure 3
Replacing sensors before catalytic converter: Oxygen sensors are located in the exhaust manifold. Remove the engine covers.
See our tech article on engine covers removing. Locate the oxygen sensor electrical connectors at the right side of the engine above the exhaust manifold. Label or mark the wiring harness to aide during reinstallation. I suggest replacing one sensor at a time so you do not mix up connectors. Using an oxygen sensor socket, loosen the oxygen sensor connection to the exhaust manifold. Do not unscrew yet.
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Figure 4
Replacing sensors before catalytic converter: Pull the wiring harness out of the mounts (green arrows) along the valve cover. Bank 1 sensor 1 shown, bank 2 sensor 1 is similar.
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Figure 5
Replacing sensors before catalytic converter: Next, disconnect the electrical connector of the oxygen sensor you are replacing (yellow arrow). First, remove the electrical connector from the mounting bracket (green arrow) by pulling straight up. Once out, disconnect the electrical connector by pressing the release tab and pulling it apart. Note the wiring harness color and the factory sensors color code sensors to help when replacing. Locate the color of the sensor you loosened. Using an oxygen sensor socket, remove the oxygen sensor from the exhaust manifold. Lightly coat the new oxygen sensor thread with anti-seize compound. Install the new oxygen sensor and tighten to 50Nm (37 ft-lb). Then reroute the wiring harness and connect the electrical connector. Repeat if replacing both sensors. Then reassemble the engine covers and clear any engine fault codes using a BMW scan tool.
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Figure 6
Replacing sensors after catalytic converter: Oxygen sensors are located in the exhaust, behind the catalytic converters. Working below the transmission, remove the transmission splash shield.
See our tech article on lower splash shield replacing. Using an oxygen sensor socket, remove the oxygen sensor connection to the exhaust manifold. When reinstalling the sensor, do not allow the harness to remain twisted (green arrow). Be sure it is properly routed and tension free.
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Figure 7
Replacing sensors after catalytic converter: Next, disconnect the electrical connector of the oxygen sensor you are replacing. First, remove the electrical connector from the mounting bracket (green arrow) by pulling it straight out toward the left side of the engine. Once out, disconnect the electrical connector by pressing the release and pulling it apart (inset). Note the wiring harness color, factory sensors color code sensors to help when replacing. Locate the color of the sensor you loosened. Using an oxygen sensor socket, remove the oxygen sensor from the exhaust manifold. Lightly coat the new oxygen sensor thread with anti-seize compound. Install the new oxygen sensor and tighten it to 50Nm (37 ft-lb).
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Figure 8
Then reroute the wiring harness and connect the electrical connector. Repeat if replacing both sensors. Then reassemble the engine covers and clear any engine fault codes using a BMW scan tool.
If your check engine light is on and you have a diagnostic trouble code P0135 stored in the PCM's memory... then you've come to the right place to test and troubleshoot the upstream oxygen sensor.
first. See our article Automotive Circuit Testing 101, if you need more assistance with this. If concern is determined to be intermittent, check out our article on Intermittent Diagnosis and wiggle test connectors and wiring, attempting to duplicate concern. You may also use the "Get Help" link if you need specifications or have any other related questions. Remember to refer to an appropriate manual for specific instruction.
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