CPS (Camshaft Position Sensor) is a system on the 7.3 Powerstroke that detects the camshaft’s revolution to signal to the truck that the motor is running well.
In other words, it counts the number of times the camshaft turns and says to the truck, “Okay big guy, everything is working fine down here, keep running.” A common symptom of a faulty CPS is that the truck completely fails to come on or a non-moving tachometer.