Friday, February 24, 2012

Crankshaft Position Sensor Operation?

The details are as follows :---

Crankshaft Position (CKP) Sensor


OPERATION



7X Crankshaft Position Sensor
EXCEPT 3.5L (VIN H) AND 3.8L ENGINES
The 7X Crankshaft Position (CKP) sensor provides a signal used by the ignition control module. The ignition control module also uses the 7X CKP sensor to generate 3X reference pulses which the PCM uses to calculate RPM and crankshaft position.
The 7X CKP sensor is the most critical part of the ignition system. If the sensor is damaged so that pulses are not generated, the engine will not start!
The 7X CKP sensor is a Hall-Effect switch, mounted on the outside of the engine block, close to the crankshaft. The interrupter ring is a special wheel cast on the crankshaft that has seven machined slots, six of which are equally spaced 60 degrees apart. The seventh slot is spaced 10 degrees from one of the other slots. As the interrupter ring rotates with the crankshaft, the slots change the magnetic field. This will cause the 7X Hall-Effect switch to ground the 3X signal voltage that is supplied by the ignition control module. The ignition control module interprets the 7X ON-OFF signals as an indication of crankshaft position. The ignition control module must have the 7X signal to fire the correct ignition coil.
The 7X CKP sensor uses a two wire connector at the sensor and a three-way connector at the ignition control module.
24X Crankshaft Position Sensor
EXCEPT 3.5L (VIN H) AND 3.8L ENGINES
The 24X Crankshaft Position (CKP) sensor is used to improve idle spark control at engine speeds up to approximately 1250 RPM. The 24X CKP sensor contains a Hall-Effect switch. The magnet and Hall-Effect switch are separated by an air gap. A Hall-Effect switch reacts like a solid state switch, grounding a low current signal voltage when a magnetic field is present. When the magnetic field is shielded from the switch by a piece of steel placed in the air gap between the magnet and the switch, the signal voltage is not grounded. If the piece of steel (called an interrupter) is repeatedly moved in and out of the air gap, the signal voltage will appear to go ON-OFF-ON-OFF-ON-OFF. Compared to a conventional mechanical distributor, the ON-OFF signal is similar to the signal that a set of breaker points in the distributor would generate as the distributor shaft turned and the points opened and closed.
In the case of the electronic ignition system, the piece of steel is a concentric interrupter ring mounted to the rear of the crankshaft balancer. The interrupter ring has blades and windows that, with crankshaft rotation, either block the magnetic field or allow it to reach the Hall-Effect switch. The Hall-Effect switch is called a 24X Crankshaft Position sensor because the interrupter ring has 24 evenly spaced blades and windows. The 24X CKP sensor produces 24 ON-OFF pulses per crankshaft revolution.
The 24X interrupter ring and Hall-Effect switch react similarly. The 24X signal is used for better resolution at a calibrated RPM.
The 24X CKP sensor clearance is very important. The sensor must not contact the rotating interrupter rings on the crankshaft balancer at any time, or sensor damage will result. If the balancer interrupter rings are bent, the interrupter ring blades will destroy the sensor. If the 24X CKP sensor replacement is necessary, the crankshaft balancer must be removed first (as outlined in of this guide). When reinstalling the balancer, torque the balancer attachment bolt to specification. This is critical to ensure the balancer stays attached to the crankshaft. If the 24X CKP sensor assembly is replaced, check the crankshaft balancer interrupter rings for any blades being bent. If this is not checked closely and a bent blade exists, the new crankshaft position sensor can be destroyed by the bent blade with only one crankshaft revolution!
Dual Crankshaft Position Sensor
3.5L (VIN H) ENGINE
The Crankshaft Position (CKP) sensor used on this engine is actually two sensors within a single housing. Each sensor has a separate power, ground and signal circuit. The PCM supplies 12 Volts to both sensors. The PCM provides the ground path, or sensor return circuit, from both sensors. These power and ground circuits are also connected to the Camshaft Position sensor. Two separate signal circuits connect the CKP sensor and the PCM. The PCM can use three different modes of decoding crankshaft position. During normal operation, The PCM performs an Angle Based calculation using both signals to determine crankshaft position. The dual sensor allows the engine to run even if one signal is lost. If either signal is lost, the PCM switches to a Time Based method of calculating crankshaft position. If the system is operating in Time A mode, the PCM is using only the signal from Sensor A. Time B indicates that the Sensor B signal is being used. If the lost signal is restored, the PCM will continue to operate in Time based mode for the remainder of the current key cycle. The PCM will revert back to the Angle mode on the next start if the fault is no longer present. A technician's scan tool can display the Crank Position Sensing Decode Mode. A problem with either Sensor A or Sensor B will set a Diagnostic Trouble Code.
The Crankshaft Position Sensor Learn Procedure must be performed after replacing the CKP sensor. Even if the original sensor is reinstalled, the Learn Procedure must be performed. This procedure must be performed with a scan tool. The crankshaft position system variation compensating values are stored in the PCM non-volatile memory after a learn procedure has been performed. If the actual crankshaft position system variation is not within the crankshaft position system variation compensating values stored in the PCM, a diagnostic trouble code may set.
The Crankshaft Position System Variation Learn Procedure should be performed after any of the following conditions:


DTC P1336 is set
The PCM has been changed
The PCM has been reprogrammed
The engine has been replaced
The crankshaft has been replaced
The Crankshaft Position Sensor has been replaced

3.8L ENGINES
On the 3.8L engines, the Crankshaft Position (CKP) sensor provides a signal used by the ignition control module to calculate the ignition sequence. The ignition control module also uses the crankshaft position sensor signals to initiate 18X and 3X reference pulses which the PCM uses as reference to calculate RPM and crankshaft position.
The dual crankshaft position sensor used on 3.8L engines is secured in an aluminum mounting bracket and bolted to the front left side of the engine timing chain cover, partially behind the crankshaft balancer. A 4-wire harness connector plugs into the sensor, connecting it to the ignition control module. The dual crankshaft position sensor contains two Hall-Effect switches with one shared magnet mounted between them. The magnet and each Hall-Effect switch are separated by an air gap. A Hall-Effect switch reacts like a solid state switch, grounding a low current signal voltage when a magnetic field is present. When the magnetic field is shielded from the switch by a piece of steel placed in the air gap between the magnet and the switch, the signal voltage is not grounded. If the piece of steel (called an interrupter) is repeatedly moved in and out of the air gap, the signal voltage will appear to go ON-OFF-ON-OFF-ON-OFF. In the case of the electronic ignition system, the piece of steel is two concentric interrupter rings mounted to the rear of the crankshaft balancer.


Click image to see an enlarged view
Fig. Because of their different blade and window configurations, the two Hall-Effect switches generate 18 and 3 CHP pulses for each crankshaft revolution-3.8L Engines
Each interrupter ring has blades and windows that either block the magnetic field or allow it to close one of the Hall-Effect switches. The outer Hall-Effect switch produces a signal called the CKP 18X because the outer interrupter ring has 18 evenly spaced blades and windows. The CKP 18X portion of the crankshaft position sensor produces 18 ON-OFF pulses per crankshaft revolution. The Hall-Effect switch closest to the crankshaft, the CKP Sync portion of the sensor, produces a signal that approximates the inside interrupter ring. The inside interrupter ring has 3 unevenly spaced blades and windows of different widths. The CKP Sync portion of the crankshaft position sensor produces 3 different length ON-OFF pulses per crankshaft revolution. When a CKP Sync interrupter ring window is between the magnet and inner switch, the magnetic field will cause the CKP Sync Hall-Effect switch to ground the CKP Sync signal voltage supplied from the ignition control module. The CKP 18X interrupter ring and Hall-Effect switch react similarly. The ignition control module interprets the CKP 18X and CKP Sync ON-OFF signals as an indication of crankshaft position, and the ignition control module must have both signals to fire the correct ignition coil. The ignition control module determines crankshaft position for correct ignition coil sequencing by counting how many CKP 18X signal transitions occur, that is, how many ON-OFF or OFF-ON, during a CKP Sync pulse.

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