The Basics of Crank and Cam Sensors and How to Test Them
Contents
1. 1 The car or truck s battery must be fully charged 2 A Digital Multimeter that can read Hertz Frequency 3 A good Repair Manual The Repair Manual will probably be just one of many information resources that you ll use to diagnose the CKP or CMP Sensors on your car or truck 4 You ll need someone to help you crank the car s or truck s engine while you observe the readings on the Multimeter A Fuel Injector Noid Light You don t need an Automotive Scan Tool commonly known as a Scanner You don t need oscilloscope N O Do I need an Automotive Scan Tool to test the CKP and CMP Sensors I ve already covered this ground a bit but I ll restate that these sensors are tested without a Scan Tool Now before ruffle some feathers let me explain that the majority of cars and trucks on the road will not set a Crankshaft Position Sensor code when the sensor goes BAD This is not an absolute truth mind you But in my experience about 95 percent of the BAD Crankshaft Position Sensors that I ve replaced the vehicle s onboard self diagnostics didn t leave any type of CKP Sensor code As you might already know such a code or codes can give you an idea of what is going on and or where to start the diagnostic process OK even if you tried using a Scan Tool most makes and models will not let you have access to the live Data to read the RPM s that the Scan tool provides while you re cranking the car or truck So if you have no li2. knowing this info will help you see the light How do the CKP and CMP Sensors Work Since each of the two and three wire types of CKP and CMP Sensors produce a different type of Signal I ll be explaining how both types work Now realize that you re not wanting to know how to build one from scratch or how to reverse engineer one so won t go into all of the details of what materials they re made of nor the fundamentals of electromagnetism that apply to these sensors nor the minute details of how they produce their Position Signal a good Automotive Technology textbook or Wikipedia and or the rest of the Internet is where you can find this information if you need it You ll learn just the nuts and bolts to test them in the real world I ll start with the two wire CKP and CMP Sensors These types of sensors are commonly known by several names Magnetic Pulse Generator Variable Reluctor Pickup Coil etc It doesn t matter what they re called or where in the car or truck they re located in they are all tested with a Multimeter in AC Volts mode Why Well because the Signal that these sensors generate is an Analog Voltage Signal and this Signal can only be measured in AC Volts mode on your Multimeter or Oscilloscope How do the Two Wire Type CKP Sensors Work When the Magnetic Pulse Generator type remember this is just one of the fancy names for the two wire type sensors is excited by the toothed disc it s in close pr
3. Frequency Hz mode to verify the Signal e The rule of thumb if you re using Volts DC mode is that this Signal should output the amount of Voltage that come s into the Sensor on the Power Circuit So when you crank the engine you should see anywhere between 9 to 12 Volts e Ifthe CKP or CMP Sensor is BAD you ll get no reading Basic Circuit Description of a Two Wire Sensor Since this type of Sensor only has two wires and no Power Supply testing them is not that hard 1 2 One of the two wires is the Signal wire that sends the Signal to the Fuel Injection Computer of Ignition Module The other wire acts as a Ground return This Ground is always provided by the Fuel Injection Computer or the Ignition Control Module On this type of Sensor you ll connect both Multimeter Leads to both wires That is the Red Lead can be connected to either of the two The Black Lead is connected to the remaining one It doesn t matter which Lead goes where since the polarity does not matter Your Multimeter has to be in Volts AC mode to see this Signal When your helper cranks the engine the Multimeter will display about 1 Volt AC Usually this AC Voltage will move between 3 Volts AC to 1 Volt AC the whole time the engine is cranking this is normal If the Sensor is BAD the Multimeter will not display any AC Voltage e This Voltage increases with Engine RPM s So the faster the engine cranks the higher the AC Voltage What
4. are the Actual Testing Steps Testing a CKP Sensor isn t hard and the diagnostic flow is pretty straightforward The following testing path applies to a Cranks but does NOT START condition Although the following tests only apply to a Crankshaft Position Sensor that has failed completely with some modification you can also follow the same diagnostic path in diagnosing a CMP Sensor 1 Step One e Make certain that the Battery is in a fully charged condition e Test for Spark o You ll need to test for spark at all cylinders to acertain that there s no Spark present at all o If Spark is present the Crankshaft Position is working properly e Test for Fuel Injector Pulse although depending on the fuel system design this is not always possible o Ifthe Fuel Injector Pulse is present the Crankshaft Position Sensor is working properly 2 Step two e Find the location of the Crankshaft Position Sensor e Determine type of CKP Sensor either a two or three wire type 3 Step three e On three wire type CKP Sensors o Determine which wire is the Power Circuit o Determine which wire is the Ground Circuit o Determine which wire is the Signal Wire e On two wire type CKP Sensors e You don t have to determine which wire is which since you don t have to test for a power supply Also the Multimeter s leads are hooked up to both wires at the same time to read the Signal the Sensor produces 4 Step four e On three wire type CKP Sen
5. sensor s signal as the Triggering Signal Since the Crank Sensor or Cam Sensor is the one producing this Triggering Signal 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
6. The Basics of Crank and Cam Sensors and How to Test Them 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 Photo 3 of 3 This Crank Sensor belongs to a 95 Toyota Tercel One arrow points to the Crank Sensor and the other to the toothed wheel that excites it 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 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 comple
7. crank sensor in this Nissan ignition system e Power Transistor Test amp Ignition Coil Test 3 3L Nissan Altima 1996 2004 o The cam sensor is actually the crank sensor in this Nissan ignition system
8. disc it s in close proximity to Now in case you re wondering if you need an oscilloscope to test these Crank and Cam Signals the answer is no You don t need an oscilloscope and you definitely don t need an Automotive Scan tool to test the CKP Sensor or CMP Sensor Signals Now having said that the absolute best way to test verify the presence of these signals is with an oscilloscope but since most folks don t own one this article concentrates on using a Digital Multimeter that can read Hertz Frequency OK now for the really important working theory part that you need to remember is that the CKP and CMP Digital Signals can be measured with a Multimeter either in DC Volts mode or in Hertz Frequency Mode or with an oscilloscope and that they need an external power source to create their signal As a side note a simple LED light can also be used to verify this signal although this method is not a 100 foolproof way of diagnosing a CKP or CMP Sensor What Excites the Sensor to Produce its Signal Before leaving the working theory alone need to talk about one more thing I m sure you ve noticed the term toothed disc thru out this article This is some sort of disc with teeth that resembles a gear or a wheel with shutters on it This disc is what excites the Sensor into producing its signal These discs go by names such as shutter wheel reluctor wheel armature interrupter ring and the like The name d
9. e your particular car s or truck s Crank or Cam Sensor is at this is where owning a good Repair Manual comes in handy or Googling it on the internet Symptoms of a BAD Crankshaft Position Sensor We can take for granted that when a CKP Sensor goes BAD your vehicle will not start It ll crank but not start But hey a car or truck could not start due to a ton of different reasons like a BAD Fuel Pump a BAD Ignition Coil a BAD Ignition Control Module BAD Spark Plug Cables etc Therefore it s not enough to say that your car or truck won t start what you need to know are some of the measurable testable effects symptoms that a BAD Crankshaft Position Sensor has on the Ignition System And so if the Crankshaft Position Sensor isn t creating a Signal then the measurable testable effects of this condition are but not limited to 1 No Fuel Injector Pulse 2 The Triggering Device whether it s the Ignition Control Module or the F I Computer will not produce a Switching Signal to the Ignition Coil 3 No Spark coming out of the Ignition Coil or Coils 4 On some makes like Chrysler Dodge Jeep the Fuel Injection Computer will not continue to power the Fuel Pump or the Ignition System with 12 Volts after an initial ten seconds or so What Tools do I Need to Test the Crankshaft and Camshaft Positions Sensors You don t need expensive tools and or expensive testing equipment to test these CKP and CMP Sensors Here s what you ll need
10. epends on who built the vehicle and or the specific type of Position Sensor being used These toothed discs rotate only when the engine is cranking and or running They are directly or indirectly connected to the Crankshaft or Camshaft Although they all perform the same basic job of exciting the CKP or CMP Sensor they come in all shapes and sizes which are determined by the needs of the software and hardware of the Fuel Injection System installed in the vehicle Well it doesn t really matter what they look like and it definitely doesn t matter one bit what they re called The important thing to know is that the sensor works in conjunction with some sort of toothed disc to produce its signal Where are The CKP and CMP Sensors Located These Sensors are located in several different places depending on the year make and or model that you re working on Some of them are in very hard to reach places and this in my opinion is the only thing that complicates testing them Some of their more common locations are In the Distributors On Timing Covers Behind Timing Covers On the Engine Blocks themselves In this type of setup the sensor goes thru the Block to reach its toothed disc Examples of this are the GM 3 1 and 3 4L V6 engines 5 On transmission bell housings Chrysler Dodge and Jeep cars and trucks are the major ones that use this setup 6 Behind the Crankshaft Pulley RON Now if you don t know wher
11. ide a different type of signal to or from their respective sensors and Fuel Injection Computer or Ignition Control Module In this primer can only go as far as to give you a basic general idea of what each circuit does To find out what each circuit does wire in the CKP or CMP Sensor s connector of your specific car or truck you ll need to look at a wiring diagram of the Ignition System in a Professional Service Manual The next best place of course is to google it on the Internet Basic Circuit Description of a Three Wire Sensor On this type of sensor each of the three wires has a specific job to do Here s the breakdown 1 2 3 One wire is the Power Source and it normally provides 12 Volts although some provide 9 Volts e You ll test for this Voltage with your Multimeter in DC Volts mode One wire is the Ground Path for the above 9 or 12 volts This Ground is generally provided inside the Fuel Injection Computer or the Ignition Control Module but not always e You ll test for this Ground with your Multimeter in DC Volts mode The third wire is the Triggering Signal wire It s thru this wire that the Crank or Cam Sensor sends the Signal it produces to the Fuel Injection Computer or Ignition Control Module e It s on this wire that you ll connect attach the Red Lead of your Multimeter to test for the Signal e The Black Lead you ll connect to ground e The Multimeter will have to be either in Volts DC mode or
12. ing 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 usually refer to the
13. ire type also known as a magnetic pulse generator type sensor among several names produces an Analog Signal By now you may be wondering what type of signal the three wire type Hall Effect type sensor produces The answer is a Digital Signal Now you might be asking yourself What the heck is a Digital Signal Let s find out A Digital Signal is a DC voltage signal remember that the Analog Signal is an AC voltage signal This DC Voltage signal looks and behaves completely different from an Analog Signal Not only that to produce this Digital DC Signal the three wire type Crank or Cam Sensor needs an external Voltage power source unlike the two wire type Crank or Cam Sensor When viewed in an oscilloscope s screen it s displayed as a square wave like the ones pictured below Photo 1 of 3 This Digital Crank Position Signal belongs to a 93 Ford Mustang A big difference compared to an Analog Signal The Digital Signal that the three wire type Hall Effect sensor type produces is a true On Off signal very unlike the Analog Signal that the two wire type sensor produces If we were to use the light bulb example from the previous page the light bulb would turn on immediately not gradually and turn off abruptly not gradually This is what causes the Sensor Waveform to look squared instead of wavy Also this turning On and Off the signal happens the entire time the Hall Effect Position Sensor is being excited by whatever toothed
14. ose switch permits us to slowly apply power or slowly take it away but never allows us to completely turn it off When you start applying the juice to the light bulb the bulb s brilliance starts to get stronger till you reach the maximum amount of power that can be applied Then you slowly start to take the power away which results in its brilliance dimming Now imagine repeating this cycle endlessly the whole time you need the room lit Well this is pretty much how the two wire type Crankshaft Position Sensors produce their signal On a last note you ve probably noticed in the slide show above that each type of Crankshaft Position Sensor waveform looks different from one another And in case you ve wondered why well this is due to the amount the shape and how far spaced apart the teeth are on the toothed disc that excites the sensor This is something that you don t have to worry about when you re testing these Crank and Cam Sensor with a Multimeter So far in this article you ve learned that all Crankshaft Position CKP Sensors and Camshaft Position CMP Sensors can be divided into two categories two wire type and three wire type Since covered the two wire type of Crankshaft Position Sensor and by extension the Camshaft Position Sensor in the first part of this article in this one I m gonna talk about the three wire type of Crank Sensor A Digital Signal for a Digital Age OK so far you ve also learned that the two w
15. oximity with it starts to produce an Analog Voltage Signal This Analog Signal is created without the help of an external power source As long as the engine is turning either because it s cranking or running the Signal is being produced When the engine is off so is the Sensor So then what is an Analog Voltage Signal As it applies to Crank and Cam Position Sensors it s a signal that oscillates between lows and highs the whole time it s being produced WITHOUT ANY ABRUPT FALLING OR RISING EDGES When the signal goes low it never completely turns off And when it goes high it must come down again This process is repeated over and over as long as the toothed disc is exciting it Looking at the oscilloscope waveforms below of three different Crankshaft Positions Sensors below will help you to put it all in perspective Photo 3 of 3 This is an Analog Signal waveform of a Crank Position Sensor of 2004 Chevrolet Malibu Did you notice in the above Crankshaft Position Sensor Signal waveforms that the AC Analog Signal produces a wavy up and down line Now to test this signal you don t need an oscilloscope But knowing what this signal looks like and how it behaves will help you to test it with a digital multimeter an analog one will work too So to further explain this concept I m gonna compare this Analog Signal to a light bulb that is cycled on and off yet never completely turning off Let s imagine that we have a light bulb wh
16. sors o Probe the Power Circuit to verify the presence of the specified Voltage This Voltage is usually verified with the key on or engine cranking o Probe the Ground Circuit to verify that ground does exist This Ground is usually verified with the key on or engine cranking o Probe the Signal Wire The presence of this Signal can only be verified with the engine cranking and with the Multimeter in Hertz Hz Frequency Mode or in Volts DC Mode e On two wire type CKP Sensors e Probe both wires coming out of the Sensor with both leads of your Multimeter The polarity of the leads doesn t matter In other words the red and black lead can go to any of the two wires e The presence of this Signal can only be verified with the engine cranking and with the Multimeter in Volts AC 5 Step Five e f no Signal is present o The Crankshaft Position Sensor is BAD replace it e Ifa Signal is present o The Crankshaft Position Sensor is good As always things on paper always seem easier than in their actual application and this is sometimes true when you re testing CKP and CMP Sensors For example in some cars and trucks it s next to impossible to verify the fuel injector pulses with a Fuel Injector Noid Light Why Well because the engineers have located them inside or underneath the Intake Manifold Plenum Don t let this deter you it s just a matter of skipping this test and going on with the rest Once you overcome these ob
17. stacles you ll find that testing them is not that hard The one thing recommend you do is to practice on a good working car to see how all of this works Well in closing if you found this article helpful please tell a friend Related Crankshaft Position Test Articles Below you ll find a list of test tutorials that will show you how to test the crankshaft position sensor for several different types of makes How to Test the Ignition Module and Crank Sensor GM 2 2L How to Test the Ignition Module amp Crank Sensor GM 2 4L Testing the Ignition Module and Crank Sensor GM 3 1L 3 4L How to Test the 24X Crank Sensor GM 3 1L 3 4L at troubleshootmyvehicle com GM 3 8L Ignition Control Module and Crank 3X 18X Sensor Test e How to Test the 3 8L GM Crank Sensor With a Multimeter at troubleshootmyvehicle com e How to Test the 3 8L GM Cam Sensor P0341 at troubleshootmyvehicle com e How to Test the Ford Ignition Control Module Distributor Mounted o This tutorial shows you how to test the PIP Sensor which is Ford s name for the crank sensor located inside the distributor e How to Test the Ford Ignition Control Module Fender Mounted o This tutorial shows you how to test the PIP Sensor which is Ford s name for the crank sensor located inside the distributor e Ignition Coil and Crank Sensor Tests 1 8L 2 4L Mitsubishi e How to Test the Cam Sensor 2 4L Nissan Altima 1997 2001 o The cam sensor is actually the
18. t you test them in action that is with the engine cranking So it goes without saying that you have to be very careful and use tons of common sense so that you won t get hurt One piece of advice that have always followed religiously and that you should too has been to have my helper wait outside of the car or truck I m testing till need him or her to crank the engine up for me This way can and have avoided losing a finger or getting hurt in case my helper thought he or she heard me say crank it and cranks the engine while still have my hands in or around the engine When piercing the Signal Wire s of the CKP or CMP Sensor you need to use wire piercing probes Why Because using a wire piercing probe is probably the safest way to keep from shorting out any of the wires that you re testing Also the wire piercing probe will always leave a small puncture wound in the wire s insulation When performing the Spark test always use a dedicated Spark Tester The only one that recommend you use is the HEI Spark Tester Everything always boils down to being alert and taking all necessary safety precautions What Does Each Wire Circuit in the Connector Do OK now to get into the meat and potatoes of testing these CKP and CMP Sensors you need to know what each wire does in the connector that attaches to the Crank or Cam Sensor Since you re dealing with two types of sensors it s logical to conclude that each circuit will prov
19. tely 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 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 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 driv
20. ve Data you won t know see if there is an RPM signal on the Scan Tool s display screen in case you didn t know the Scan Tool displays the RPM s from info from the CKP Sensor Therefore knowing how to test them with a multimeter or an LED or an oscilloscope or whatever independent of a Scan Tool becomes very important Now when it comes to Camshaft Position Sensors a Scan Tool does come in handy since a BAD CMP Sensor does register a diagnostic code This code usually lights up your check engine light on your instrument cluster But testing them requires a method that is independent of the Scan Tool and well as I ve mentioned before the test steps that apply to a CKP Sensor also apply to a CMP Sensor The other thing that really sucks when you re trying to diagnose a CKP or CMP sensor is that most of the service literature does not have very specific test information After all these service manuals take for granted that the person reading them are professional service technicians that already know the basic working theory and or tests Alright let s jump into the next part where get into some testing specifics You ve covered a lot of information so far in this section I ll get into the basic flow of tests that are part of diagnosing the Crankshaft Position Sensor and Camshaft Position Sensor Do s and Don ts When Testing CKP and CMP Sensors Testing the Crankshaft Position Sensors or Camshaft Position Sensors requires tha
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