Automotive Technology Course | Speed/Position Sensor Testing (CAM/CRK)

Automotive Technology Course | Speed/Position Sensor Testing (CAM/CRK)


you you you there are five basic types of speed position sensors the magnetic sensor which produces a sine wave the magneto resistance sensor which produces a square wave the Hall effect which also produces a square wave the reed type which is oftentimes used on vehicle speed sensor applications and finally the optical type position sensor the magneto resistive hall effect and optical sensors need their own power and ground to operate the optical sensor also uses a photo transistor to create this signal the two most common types are the magnetic or permanent magnet sensor and the Hall effect position sensor the magnetic sensor produces its own sine wave generally speaking as seen here on screen all speed position sensors are composed of the sensing tip or coil the electrical connector socket and a possible transistor housed inside the sensor casing itself magnetic sensors do not use an internal transistor all position sensors are affected in one way or another by the air gap between the sensing tip and the reluctor or toothed wheel seen here on screen the amplitude of a two-wire magnetic sensor is directly affected by the air gap between the sensor and the reluctor wheel the amplitude is also affected by the speed of rotation of the reluctor wheel magneto resistive and Hall effect sensor amplitude is not affected by the speed of rotation of the reluctor or bone ring however these two sensors are affected by the air gap between the sensor and the reluctor ring a further consideration of magnetic sensors is the bias voltage provided by the ECM these very low current bias voltage is used by the ECM to detect open end short circuit conditions however not all magnetic sensors used bias voltage use a voltmeter to verify whether a bias voltage is present Hall effect sensors which are very common work by toggling or pulling a reference voltage to ground thereby creating the square waveform this reference voltage to be toggled by the Hall effect speed sensor is provided either by the ECM or the ignition control module or ICM remember the output of a Hall effect sensor magneto resistive sensor or optical sensor is always a square wave Hall effect and magneto resistive speed position sensors employ an internal transistor to do the switching and be able to toggle the reference voltage to ground these type of sensors are oftentimes used for cam and crank applications and in modern systems also for wheel speed sensor applications the signal path of a speed position sensor is extremely important during Diagnostics there are two basic ways to pass a signal along point-to-point and by using a vehicle module in their network with point-to-point connection the speed sensor is directly connected to its own respective module with a network system the speed sensor is connected only to one of the modules and such a module is in charge of broadcasting or passing along the speed and position information to the rest of the system module yunus network systems are very popular in newer systems due to the savings in weight and less complex electronics as much as 200 pounds of weight and wires is saved by using a network system this translates to lighter and more fuel-efficient vehicle any direct aspect of speed sensor signals is the relationship between the cam and the crank sensor synchronization remember when ascertaining a relationship between these two signals there are always two crankshaft revolutions for one single camshaft revolution these two signals had to match precisely it is very common to see an engine that will not start due to a loss of synchronization between the camshaft and crankshaft the end result will be an ECM cutting pulsation to the injectors in an effort to protect the engine from mechanical damage it is useful to develop your own signal waveform library for later reference when diagnosing these systems and finally always be mindful of the speed sensor signal glitch which can also look exactly the same as a crank sensor misfire event always set your scope at a high time right in order to pack as many cycle events as possible and be able to catch the glitch or misfire a misfire or glitch would always show up best when looking at the whole picture the very first step in any sensor testing routine is to perform a visual inspection of the sensor in question this also includes its wiring and connector portion in our example we will be testing a magnetic sensor which is evident from the two terminals at the connector side magnetic sensors always employ two electrical terminals and produce a rounded wave also called a sine wave as opposed to a DC square wave square waves are produced by Hall effect magneto resistive and optical sensors step one is to start by connecting the oscilloscope or digital multimeter to the magnetic sensors two terminals magnetic sensors are usually not polarity sensitive so what to see irrelevant on how you connect the oscilloscope or graphing multimeter make sure that the oscilloscope or graphing multimeter is not internally grounding one of the leads in many cases this nun polarity condition of magnetic sensor circuits also mean that the magnetic sensor ground is not the same as battery or chassis ground even if the sensor is internally grounded by the ECM remember it may not be necessary to observe polarity when testing a magnetic speed position sensor simply makes sure that your equipment is not internally grounding one of the leaves the output of a magnetic sensor is always going to be a sine wave which is always rounded at the edges also due to the alternating current producing nature of magnetic sensors always set your scope to AC or alternating current our test vehicle is a late-model Ford Taurus with a 3.0 engine since we are measuring an alternating current cycle set your zero line on the scope to halfway of the graticule or screen this will let you measure both sides of the cycle step 2 set your time base to a value that allows you to measure the signal at idle this is usually around 2 milliseconds a higher time base setting may be needed to pack more cycles on the screen and therefore be able to catch a possible signal glitch this could be asked much as 100 to 500 milliseconds after starting the engine the magnetic sensor sine wave should immediately show up on the screen verify the two characteristics of any repeating waveform which is amplitude and frequency as a rule of thumb a minimum of two volts peak-to-peak is needed for signal recognition and a frequency should correspond to the speed of engine rotation always remember that the amplitude of a magnetic sensor will increase with an increase in engine speed this is very different from a Hall effect or magneto resistive sensor where the amplitude is always kept constant regardless of engine speed then increase the time base on the oscilloscope to be able to capture any signal glitch caused by a problem in the flywheel reluctor sensor or wiring fault keep increasing the time base on the oscilloscope to be able to pack as many cycles as possible on the screen the use of the scope recording capabilities is quite useful during a signal which capture most high quality scopes as well as the snap-on Vantage have this feature if your equipment has this capability use it it will save you time and money recording is very useful during Road testing in order to duplicate the problem capture the waveform and then bring it to the shop later on for analysis in this particular case as shown on screen the recorded signal is playback the signal which is captured and the cursors are used to make all the necessary measurements this makes for an easy way to leisurely capture and measure your problem waveform on the other hand using a low time base on the oscilloscope allows you to make the two most important measurements when analyzing any signal which are amplitude and frequency these two cannot easily be measured using a high time base the amplitude of a waveform is absolutely necessary for signal recognition a minimum of two volts peak-to-peak is needed for signal recognition by most modules on the market today and the frequency is dependent on the speed of rotation of the reluctor or flywheel as a final note you can always use the oscilloscope to check the integrity of the number one TDC timing mark on the crank sensor signal this timing mark may not necessarily coincide with cylinder number one being on top dead center this is simply a reference used by the ECM to know how close cylinder number one is from top dead center this TDC mark made replaced many degrees before or after the top edge Center event when analyzing this particular part of the waveform remember to take into consideration the actual polarity of the signal in the event that the two wires at the speed position sensor has been reversed the vehicle will not run properly the only way to know this is by comparing your waveform to a previously recorded signal of the same vehicle and here lies the importance of keeping a waveform library and don’t forget to check the camshaft and crankshaft synchronization the camshaft and crankshaft synchronization is very important on modern vehicles and unsynchronized camshaft and crankshaft signal may even cause the ECM to cut injector pulsation in order to protect the engine at the very least it may cause a faulty code which would be impossible to get rid of unless these two signals are synchronized the small gap seen here on screen corresponds to cylinder number one TDC mark remember this mark may not necessarily coincide with cylinder number one being on top dead center for every two crankshaft revolutions there is one camshaft revolution this becomes very important when analyzing camshaft and crankshaft synchronization events the problem becomes aggravated when analyzing a vehicle that has jumped only one tooth on the timing belt but this technique may be very useful when analyzing minor timing belt problems following is a brief procedure to test a magnetic camshaft position sensor the procedure is the same as when testing any other magnetic crankshaft position sensor the only difference is when analyzing the camshaft and crankshaft synchronization relationship start by connecting the graphing multimeter or oscilloscope to the magnetic sensor two wires again when measuring just the magnetic sensor signal the polarity is not important polarity is important only when analyzing the cylinder number one timing mark just make sure that your equipment is not internally grounded at the battery the voltage recognition threshold explained before applies to this magnetic camshaft position sensor as well a minimum of two volts peak-to-peak is needed for the signal to be recognized by the ECM again when analyzing cam chef 2 crankshaft relationships remember that there are two revolutions of the crankshaft for camshaft revolution you


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