How to Tell If the O2 Sensor Is Bad in a Ford Explorer

by Jody L. Campbell

Oxygen sensors have been installed into the exhaust systems of vehicles for quite a few years. Depending on the year of your Ford Explorer, you may very well have multiple oxygen sensors. The easy part is telling if one is bad; the hard part is telling which one is bad. These sensors monitor the amount of oxygen to the ratio of fuel burned through the exhaust system,l and if they detect a variation above or below a certain range, the sensor sends out a signal to the computer of the Explorer, which then triggers the MIL (Malfunction Indicator Lamp) to be illuminated on the dashboard while the vehicle is operating.

Step 1

Locate the DLC (diagnostic link connector) under the driver's-side dashboard. It will have a trapezoidal shape and resemble the outlet of the code reader plug. Plug the hand-held portable code reader into the DLC once you've located it.

Step 2

Turn the ignition key two clicks to the "key-on/engine-off" position. This will apply power to the code reader and allow all of the power options of the Explorer to perform without the vehicle actually running.

Step 3

Locate the buttons and options on the code reader. Many hand-held code readers will have two or three buttons. One will be an "Enter" button and the other one or two will be scroll buttons that will manipulate the cursor to the onscreen menu of the code reader. Use the scroll button to move up or down to the "Codes detected" or "Read codes" option on the onscreen menu of the code reader. Press the "Enter" button.

Step 4

Write down the number and the brief description the code reader dictates on the onscreen menu. An example may be "System Lean; Bank One Sensor Two." This would indicate the the mix of oxygen and fuel is too lean and the sensor in the first bank and farthest from the engine has triggered the MIL light to report the problem to you. While this is merely one example of many different DTCs (diagnostic trouble codes) that could trigger an MIL light to illuminate, it does indicate a problem with the oxygen sensor and which one has the problem.

Step 5

Locate the bad oxygen sensor by referring to the manual to learn where the first cylinder or "Cylinder One" is located on the motor. Different-sized motors in the Explorers offer a variety of options. The position of the first cylinder dictates which bank the oxygen sensors run and scan. It may be the right side or it may be the left side. Some Explorers may have up to four oxygen sensors, and determining the bank is crucial to locate and condemn the problem sensor. The lower the number in the bank position (for example, bank one) the closer to the motor the sensor would be. The higher the number in the bank position (bank two), the farther down the exhaust system and away from the motor it will be.

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