Explorer Oxygen Sensor Issue

The symptoms point to a possible oxygen sensor issue. Use an OBD II scanner to get the specific error code. This will tell you which sensor is the problem (upstream or downstream). Also, check the live data stream from the oxygen sensors. Look for abnormal voltage fluctuations or a slow response. Do you have a multimeter to check the sensor's heater circuit resistance?

I have a multimeter and checked the wiring harness for continuity; all sensors seem to have power. I'm worried about a bad plug connection. How can I confirm the sensor failure before buying a replacement? I don't want to replace a sensor that's working.

Since the wiring and power are okay, a defective plug connection is possible. Corrosion or damage to the connector pins can disrupt the signal. You could try electrical contact cleaner on the exhaust sensor plug connections, and make sure they fit tightly. But, given the stored error, it might be best to have a workshop handle the replacement. An aged sensor replacement should be around 95€, including diagnosis, replacement, and clearing the error code, and should restore your fuel efficiency.

Based on your advice and further checks, the problem was an old oxygen sensor with a bad plug connection. I took it to a workshop and after paying 95€, it's fixed!