Your GMC oxygen sensor is a heat lover! In fact it needs to be heated to activate, and then to send a signal to your GMC Engine Control Unit about the oxygen and fuel levels in your combustion system. On average, the GMC oxygen sensor needs to be about 600 degrees Fahrenheit to operate correctly. Most oxygen sensors are hooked up to a 12V heater to preheat the sensor, which is usually located in the already blazing-hot manifold. An oxygen sensor that is pre-heated will be quicker to respond, and boost your fuel efficiency. Some sensors with heaters come with three or four wires that hook up to the heater, ground the sensor and send a message to the ECU. Once the sensor is heated, positive voltage is generated between the two layers of platinum that make up the inner and outer layer of the oxygen sensor. One layer measures the oxygen levels in the exhaust of your GMC, the other layer measures the oxygen levels in the interior of the sensor. Depending on the difference between these two measurements, the sensor will send a message to the ECU in the form of voltage. The heat activates the GMC oxygen sensor to complete the open loop between the sensor and the ECU.