The first step in the installation is to back-probe the connections to the coolant temp sensor, either at the ECU or near the sensor itself. (On the Maxima we did it near the sensor because it was quicker and easier to find the right wire without having a dedicated workshop manual). As mentioned, you’re looking for a voltage (normally between 0-5V) that decreases as the car warms up. So you can easily see this change, start off the measuring process with the engine cold. Here the voltage shown on the meter is 2.369V – it was falling rapidly as the car warmed up.