Crankshaft Position (CKP) Sensors and Camshaft Positions (CMP) Sensors used on cars and trucks today come in all sorts of different shapes, sizes and configurations. All this variety might make you think that testing them is difficult and/or impossible. Well, nothing could be further from the truth since they can be easily tested with simple tools and testing techniques.
This article is a primer that will help you to learn and understand the essentials of testing the Crankshaft Position Sensor (Camshaft Position Sensors too). You'll learn basic working theory, do's and don'ts, what tools to use and how to test them, and a lot of other good stuff.
At the end of the article, in the section titled: Related Crankshaft Position Test Articles, I have included a list of test tutorials that will show you how to test the crank and/or cam sensor on several different makes (GM, Ford, Nissan, etc.) based on the info in this article.
How to Tell Them Apart
Another thing that can make testing the CKP and CMP Sensors seem intimidating is the fact that every make and model rolling around on pavement uses a different type of Position Sensor. For example, the Ford truck your neighbor might be driving will have a Position Sensor(s) that is (are) completely different in appearance than your GM (or Chrysler, or Honda, or Nissan or Suzuki, etc.) vehicle.
Not only that, but these sensors are called by so many different names like: Hall Effect Sensor, CKP Sensor, CMP Sensor, Pickup Coil, Magnetic Pulse Generator, Variable Reluctor, and the list goes on with a few more names. This may make it seem like every single one is tested in a different way. Well, the good news is that although they all differ from one another physically and are called so many god-knows-what names, they can usually be generalized into two basic categories: 2 wire type and 3 wire type. And this means that you only have to learn two specific testing methods.
So, before we dive into the rest of the article, I want to emphasize that the key to successfully testing and diagnosing all of the different Crank Sensors (and Cam Sensors) out there, is to know if they are either a two or three wire type! Now in case you're wondering what I mean by two and three wire types... I'm referring to the amount of wires in their connector (of course there's always an exception to every rule, but more about this later). Alright, let's jump into the next subheading and let's start learning more about this.
What does a Crankshaft (Camshaft) Position Sensor Do?
I'll start by explaining the specific role that the Crank (and Cam) Sensor play in the Electronic Ignition System of your car or truck. This info applies to whatever make and model you may be driving, so whether it's a Ford, a Chevy, a Chrysler/Dodge/Jeep, a Nissan, a Honda, a Toyota, or whatever, this primer will help.
In a nutshell, the Crankshaft Position Sensor's job is to help: 1) the Ignition System produce Spark and 2) the Fuel System to start injecting gasoline into the cylinders. All this so that the vehicle's engine will start and stay running. More specifically, the CKP Sensor produces a signal that tells the Fuel Injection Computer or the Ignition Control Module the exact position of the cylinder pistons as they come up or go down in the compression cycle. With this information the Fuel Injection Computer or the Ignition Control Module knows the exact time it has to make the Ignition Coil or Ignition Coils spark (not to mention when to start injecting fuel into the cylinders). Lastly, this signal can be either an Analog Voltage Signal of a Digital DC Voltage Signal... but more about this a little later.
The Camshaft Position Sensor is GENERALLY used in all modern Sequentially Fuel Injected engines to fine tune ignition timing and fuel injection timing after the vehicle has started. Although this article concentrates on the basics of Crankshaft Position Sensors, you can apply most of this info to the Camshaft Position Sensors too.
Since the Crankshaft Position Sensor's Signal triggers the Ignition Module (or Fuel Injection Computer) to start switching the Ignition Coil's Primary Current ground path On and Off... I usually refer to the sensor's signal as the Triggering Signal. Since the Crank Sensor (or Cam Sensor) is the one producing this Triggering Signal, I refer to it as the Triggering Device.
The signal that the Ignition Module (or Fuel Injection Computer) sends the Ignition Coil for it to start sparking is the Switching Signal. So, guess what... the Ignition Module (or the Fuel Injection Computer) is therefore the Switching Device.
Now, the Ignition Control Module really doesn't send a physical signal (like the Crank or Cam Sensor does to the Switching Device) to the Ignition Coil(s). Why? Well, because the term ‘Switching Signal’ is just a descriptive name for the turning on and off of the primary current passing thru' the Ignition Coil. And as stated above, this turning on and off only happens after the Ignition Module (or Fuel Injection Computer) receives the Crankshaft Position Sensor's Signal. As you may already know, it's this action that causes the Ignition Coil to start firing Spark.
You don't need to memorize all of these details, but it's very important to understand them. Why? Well because understanding and knowing how one Signal leads to the creation of another type of Signal will help you to diagnose a ton of makes and models. Or when you run across a specific testing step in your auto repair manual or in this site or any other that is not explained in painstaking detail (and you're feeling lost as to the ‘why’ of the test you just were asked to perform), knowing this info will help you see the ‘light’.