How to Replace an Oxygen Sensor

Twelve years and more than 100,000 miles have passed under your trusty commuter and the Check Engine light has never, ever, winked at you ... until yesterday, when it coincidentally anticipated your state inspection appointment at the end of the month. Rats! The car will never pass the emissions test with that light on. Now what?


Here's the perfect opportunity to break out that new, easy-to-use, consumer-grade OBD II (On-Board Diagnostics II) generic code reader. That's what we did on our sacrificial lamb, a Nissan Altima. After plugging in the universal connector under the dash, we retrieved a code P0136 "O2 Sensor Circuit Malfunction (Sensor


2)." This let us zero in on the likely problem right away. Remember, a trouble code stored in the engine computer doesn't necessarily tell you what's wrong. It's just a good starting point.

So, it's time to actually check out the sensor. Sensor 2 is the downstream sensor, in the catalytic converter, smack in the middle of the underside of the car. Start by getting the car up on some safety stands, then roll underneath it with a creeper.

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