The ECT sensor is located on the coolant crossover pipe which is located at the rear of the engine and is bolted to the rear ends of the two cylinder heads. On 2003 through 2006 G35 Sedans and 350Z models and all G35 Coupes, the ECT sensor is located behind the right cylinder head, near the flange where the crossover pipe is bolted to the right cylinder head. On 2007 and later G35 Sedans and 350Z models, the coolant crossover pipe is slightly different in appearance than the pipe used on earlier models, and the ECT sensor is located at the left end of the crossover pipe, near the flange where the crossover pipe bolts to the left cylinder head. Partially drain the cooling system, to a level that's slightly below the cylinder heads. Disconnect the electrical connector from the ECT sensor. To remove the ECT sensor, depress the release tab and disconnect the electrical connector, then unscrew the ECT sensor from the coolant crossover pipe. Using a deep socket, unscrew the ECT sensor from the coolant crossover pipe. Install a new sealing washer on the sensor. Installation is otherwise the reverse of removal. Be sure to tighten the ECT sensor to the torque. Refill the cooling system.