What is the purpose of a reference voltage?

What is the purpose of reference voltage? Welcome to Mercie J Auto Care, where compassion and craftsmanship come together, I'm Rick Smith. So I want to First tell you that this video is a little bit more directed towards technicians than our regular client base. I'll just throw a little joke in there, “V ref” when you see that on a wiring diagram that means reference voltage. Now V ref on an airplane, that's the speed of the aircraft upon landing. So that's a different ball game and you can talk to a professional pilot to know what v Ref is for the airline industry. So on our typical three-wire sensors, we can use sensors to measure a number of things. We can use them to measure temperature, we can use them to measure the position of something like the throttle or even a window. We can use them to measure the speed something's turning like a crankshaft sensor or the wheel speed sensors, things like that. We can also use them to measure pressure, like vacuum in the intake manifold or pressure in the air conditioning system. We typically will have two or three wire sensors. Reference voltage that I'm talking about today is typically on a three wire sensor and in a typical situation what we do is we send five volts out from the computer. Then the computer uses a ground and then as we vary that sensor there's a signal wire that comes back that changes that five volts. Now that 5 volts needs to be pretty accurate between 4.9 and 5.1. So as an example, today we have a 2007 Ford Explorer and it runs very poorly and it has a ton of different codes. Now I checked the voltage reference at a number of different places and instead of being five volts, it's about two and a half to three. So now I can either start unplugging different sensors like the AC pressure, the throttle, a number of different things. In this case as I traced it down, I actually ended up cutting the wire going back to the tank or the fuel tank pressure sensor and my five volts came back, the rest of the sensors came to life and the vehicle started running properly. So I either have a shorted wire back there by the tank or a bad fuel tank pressure sensor pulling that voltage down. Once I drop the tank, I'll be able to identify which of those it is. So I hope this helps you understand a little bit about that v ref but when you check it on the three wire sensor, 4.9 to 5.1. If that's not what you have, then you need to find out why. I hope this has been informational to you, until next time, safe travels and blessings to you.