Cam shaft position sensor

<p><b><span>3.2) <span> </span><u>CMP - Cam shaft Position </u>(sensor)<u> </u></span></b><br /> <p><b><u><br /></u></b><br /> <p><b><span>What is it?</span></b><span><span> </span>This electrical device is very similar in concept to the crank position sensor (above) in that it detects the position of the rotation of a shaft, in this instance the cam shaft.<span> </span>It is the cam shaft signal that indicates to the ECU that cylinder one is at top dead centre at compression and in the process provides the ECU with the timing reference for fuel injection.<span> </span>The cam shaft sensor provides extra information, to that of the crank sensor, to fine tune timed events such as injection and spark delivery.</span><br /> <p><span> </span><br /> <p><b><span>Where is it located?</span></b><span> The location of this device depends on the design and age of engine.<span> </span>On many modern overhead cam shaft engines the cam shaft sensor is located either on the end, or to the side of the end, of the cam shaft housing.<span> </span>On older pushrod engines the cam sensor is found where the distributor would once have been located.<span> </span>This type sensor assembly makes use of the distributor shaft meshing directly, at its bottom end, with a gear on the cam within the engine block.<span> </span>In this respect the distributor shaft is just an extension of the cam shaft.<span> </span>On the top end of this distributor shaft is a magnetic armature.<span> </span>The cam shaft sensor, that measures the movement of this armature, is located in the cover and uses either magnetic or 'Hall effect' pickup modules.<span> </span></span><br /> <p><b><span> </span></b><br /> <p><b><span>How does it work?</span></b><span><span> </span>The sensor detects the position of a magnet or set of teeth on the gear on the end of the cam.<span> </span>An electrical waveform output signal is sent to the ECU as the cam turns.<span> </span>The cam sensor tells the ECU that cylinder 1 is at TDC on its compression stroke prior to ignition. <span> </span>The cam sensor ensures the correct timing of the fuel injection cycle.<span> </span>If the timing belt ever jumps a tooth on the cam the lack of agreement between the respective signals from the cam and crank sensors is indicated as an error condition by the ECU. </span><br /> <p><b><u><span><span> </span></span></u></b><br /> <p><b><u><span>Symptoms of faulty cam sensor</span></u></b><br /> <p><b><span>Associated OBD2 error codes DTCs: <span> </span>P0341 - P0349; P1345</span></b><br /> <p><b><span> </span></b><br /> <ul> <li><b><span>Hesitant acceleration - </span></b><span>miss-timing of fuel injection due to a faulty CMP can cause intermittent loss of power.<b></b></span></li> <li><b><span>Starting difficulty/failure.<span> </span></span></b><span>If the faulty CMP timing problems are severe they may cause the engine not fire at all, or to fire and then stall, or stall at some random time without warning.<b></b></span></li> <li><b><span>Hot engine stall and failure to restart - </span></b><span>Sometimes the fault of the CSS only manifests itself when the engine is hot.<span> </span>Over time thermal stress can cause cracking and can weaken electrical junctions within the CMP.<span> </span>The CMP may work well at cold start up but can then cause a hot running engine to stop with little chance of restart whilst the engine is still hot;<span> </span>once cooled the down the engine may readily restart and again run for a limited period until hot.</span></li></ul> <p><b><u><span>Note </span></u></b><span>The cam sensor body often protrudes into the cam shaft gallery and when it's 'o' ring seal<span> </span>becomes age hardened, engine oil may leak back into the sensor electrical socket plug connector causing errors due to interruption of signal. </span><br /> <p><b><span> </span></b><br /> <p><b><span>How to check? </span></b><span>It is not technically<b> </b>easy<b> </b>to determine that the CMP is at fault and, like the crank sensor, may require the use of an oscilloscope.<span> </span>If it is part of a sophisticated on board diagnostics system its failure may be logged as a specific error code in the ECU. Due to the variability problems with engine running are often experienced well before any error codes are set by the ECU.</span><br /> <p><span> </span><br /> <p><span><span> </span>2 pin socket (magnetic - sine wave output).<span> </span>One pin is 'ground' the other is 'signal'.<span> </span>A voltmeter set to 2 volts AC should measure a signal in the 0.2 to 2 volts range on the 'signal' pin.</span><br /> <p><span><span> </span>3 pin socket (Hall effect, magneto - square wave form output).<span> </span>One pin is 'reference' (5volts), one pin is 'ground' and the third pin is 'signal'.<span> </span>A DC voltage should be detectable in the 0.5 to 1.5 volt range from the 'signal' pin.</span><br /> <p><span>It is important that the voltage measurement take place at start up when the engine is cold and again, 20 minutes later, when the engine has fully warmed up to operating temperature. Often the voltage output from faulty sensors declines with temperature rise.</span><br /> <p><span> </span><br /> <p><b><span>How to fix?<span> </span></span></b><span>If the CMP failure is due oil leakage into the electrical connector then a thorough clean and a renewal of the oil seal on the CMP may correct the situation.<span> </span>It can be a wise precaution to change the connecting cable as oil migration beneath the insulation may possibly contaminate components at some distance to the CMP.<span> </span></span><br /> <p><span>If the CMP has an internal fault then it must be replaced.</span><br />