Testing sensor not only helped me learn how to test them, but also how they work. Here in the above picture I'm testing a oil pressure sensor off of a CAT engine. Pressure sensors will have three wires, one green(C) for signal, one yellow(B) for 0v reference, and one orange(A) for 5v. For testing a pressure sensor just hook up 5v power to wire A and hook up wire B to ground. Then hook up the DMM positive lead to wire C and the negative lead to wire B. With power on and no additional pressure, the DMM reads 0.4441v. With the sensor hooked up to the shops air (so about 90 - 100 pis) the DMM reads 4.9980v. With a reading of almost 5v, it look like the air pressure is above what the pressure sensor reads. I tested another same type and some model of sensor, but got different readings. The reads were 0.0063v - 0.2540v, so i think this sensor is bad.

 Cutting apart the sensor changed what i thought was inside of the sensor. From what i understand the pressure compresses the round white part, witch changes the capacitance of the sensor. The ECM has pre-programed values to determine the pressure by reading the return analog signal voltage from the sensor.

 Here is a temperature sensor inserted in the right side on the vortex tool. By the way the vortex tool is a cool little tool that makes hot air and cold air at the same time. A temperature sensor has only two wires. One is a voltage reference and one ground. The ECM just reads the the resistance through the sensor as temperature changes. So I hooked up in DMM to read resistance and the other to read the temperature of the air coming out of the vortex tool. At a temp of -14.1 degrees the resistance was 19.64oms and a air temp of 164.1 degrees the resistance was -19.64oms

Here I've got a Ford throttle position sensor that has only three wires. This sensor is hooked up just like the pressure sensor. The difference is that this sensor has a potentiometer inside. Siting with the power on the DMM reads 4.5163v. Turning the position sensor clockwise all the way gives a reading of 0.3800v 

 

 

I also tested a magnetic pickup sensor. These sensors have a permanent magnetic core inside, with wire rapped around it both ends of the wire sticking out. This sensor doesn't need any power to it. The sensor generates voltages signal through the collapse of a magnetic field created by a moving metal trigger. To test it, all I did was hook the positive lead of the DMM to wire and the negative lead to the other wire. With the DMM reading voltage, I held the sensor close to rapidly spinning piece of metal. The out come was that the DMM read a small amount of volts.