GM Bonneville/Eighty Eight/LeSabre 1986-1999

Crankshaft Position Sensor

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OPERATION



See Figures 1, 2 and 3

The dual Crankshaft Position (CKP) sensor is mounted to the front of the engine, attached to an aluminum bracket mounted to the left side of the engine at the timing chain cover. A 4-wire connector plugs into the sensor, connecting it to the ignition control module. The CKP sensor contains 2 Hall effect switches with 1 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 voltage signal is not grounded. If the piece of steel (called an interrupter ring) is repeatedly moved in and out of the air gap, the signal voltage will appear to go ON, OFF, ON, OFF, ON, OFF. This ON/OFF signal is similar to the signal that a set of conventional breaker points in a distributor would generate, as the distributor shaft is turned and the points open and close.



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Fig. Fig. 1: The Crankshaft Position (CKP) sensor is mounted to the front left side of the timing chain cover

In the case of the electronic ignition system, the piece of steel is 2 concentric interrupter rings mounted to the rear of the crankshaft balancer. Each interrupter ring has blades and windows that, in conjunction with the crankshaft revolution, either block the magnetic field or allow it to reach one of the Hall effect switches. The outer Hall effect switch is called the 18X crankshaft position sensor, because the outer interrupter ring has 18 evenly spaced the same width blades and windows. The 18X crankshaft position sensor produces 18 ON/OFF pulses per crankshaft revolution. The Hall effect switch closest to the crankshaft, the 3X crankshaft position sensor, is called this because the inside interrupter ring has 3 unevenly spaced, different width blades and windows. The 3X crankshaft position sensor produces 3 different length ON/OFF pulses per crankshaft revolution. When a 3X interrupter ring window is between the magnet and the inner switch, the magnetic field will cause the 3X Hall effect switch to ground the 3X signal voltage supplied from the ignition control module. The 18X interrupter ring and Hall effect switch reacts similarly.



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Fig. Fig. 2: The crankshaft balancer has a series of interrupter rings

The ignition control module interprets the 18X and 3X ON/OFF signals as an indication of crankshaft position, and must have both signals to fire the correct ignition coil. The ignition control module determines crankshaft position for the correct ignition coil sequencing by counting how may 18X signal transitions occur, ON, OFF or OFF, ON during a 3X pulse.



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Fig. Fig. 3: Because of their different blade and window configurations, the two Hall effect switches generate 18 and 3 CKP sensor pulses for each crankshaft revolution

TESTING



See Figures 4 and 5

  1. Visually check the connector, making sure it is connected properly and all of the terminals are straight, tight and free of corrosion.
  2.  
  3. With the ignition in the ON position, check the sensor voltage using an oscilloscope. When the starter is briefly operated a square wave pattern, varying between 0-12 volts and providing 3 pulses per crankshaft revolution should be seen at terminal V. The same signal providing 18 pulses per crankshaft revolution should be seen at terminal A. If voltage is within specification, the sensor is functional.
  4.  



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Fig. Fig. 4: Crankshaft Position (CKP) sensor circuit - 1987-5 vehicles



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Fig. Fig. 5: Crankshaft Position (CKP) sensor circuit - 1998-99 vehicles

  1. If the voltage falls out of range, use a DVOM to check terminal C for battery positive (B+). If battery positive (B+) voltage is not present, check the circuit continuity and repair as necessary.
  2.  
  3. If battery positive (B+) voltage is found at terminal C, check the terminal D for proper ground. If ground is not present, check the circuit for continuity and repair as necessary.
  4.  
  5. If the sensor and circuits are functional, the PCM may be faulty.
  6.  

REMOVAL & INSTALLATION



See Figures 6, 7 and 8

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the serpentine drive belt from the crankshaft pulley.
  4.  
  5. Raise and safely support the vehicle.
  6.  
  7. Remove the right front wheel and tire assembly and the right inner fender access cover/splash shield.
  8.  
  9. Using a 28mm socket, remove the crankshaft harmonic balancer retaining bolt.
  10.  
  11. Remove the crankshaft balancer, using a puller if necessary.
  12.  
  13. For 1992-99 vehicles, remove the CKP sensor shield.
  14.  



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Fig. Fig. 6: If so equipped, remove the crankshaft position sensor shield

  1. Unplug the sensor electrical connector.
  2.  
  3. For 1987-91 vehicles, perform the following:
    1. Remove the sensor and pedestal from the block face.
    2.  
    3. Remove the sensor from the pedestal.
    4.  

  4.  
  5. For 1992-99 vehicles, remove the sensor from the block face.
  6.  

To install:
  1. For 1987-91 vehicles, perform the following:
  2.  
  3. Loosely install the crankshaft sensor on the pedestal.
  4.  
  5. Position the sensor, with the pedestal attached, on crankshaft sensor installation tool J 37089 or equivalent.
  6.  
  7. Install the bolt to hold the pedestal to the block face, then tighten to 14-28 ft. lbs. (20-40 Nm).

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    Fig. Fig. 7: Position the crankshaft sensor tool on the crankshaft



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    Fig. Fig. 8: Insert the crankshaft sensor tool into the harmonic balancer

  8.  
  9. Tighten the pedestal pinch bolt to 30-35 inch lbs. (3-4 Nm).
  10.  
  11. Remove the special tool.
  12.  
  13. Place the crankshaft sensor tool on the crankshaft balancer and turn. If any vane on the harmonic balancer touches the tool, replace the balancer.
  14.  

  1. For 1992-99 vehicles, install the CKP sensor on the block.
    1. Install the retaining bolts and tighten to 14-28 ft. lbs. (20-40 Nm).
    2.  
    3. Install the crankshaft position sensor shield.
    4.  
    5. Attach the sensor electrical connector.
    6.  

  2.  
  3. Install the balancer on the crankshaft.
  4.  
  5. Tighten the crankshaft bolt to 200-239 ft. lbs. (270-325 Nm) for 1987-91 vehicles. For 1992-99 vehicles, tighten to 110 ft. lbs. (150 Nm), plus an additional 7° rotation.
  6.  
  7. Install the inner fender shield and the right tire and wheel assembly.
  8.  
  9. Carefully lower the vehicle.
  10.  
  11. Install the serpentine belt.
  12.  
  13. Connect the negative battery cable.
  14.  

 
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