GM Corsica/Beretta 1988-1996 Repair Guide

Camshaft Position (CMP) Sensor

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OPERATION



The PCM uses the CMP sensor to determine the position of the No. 1 piston during its power stroke. This signal is used by the PCM to calculate fuel injection mode of operation.

If the cam signal is lost while the engine is running, the fuel injection system will shift to a calculated fuel injected mode based on the last fuel injection pulse, and the engine will continue to run.

TESTING



The best method to test this sensor is with the use of an oscilloscope.

2.2L (VIN 4) Engine
1996 VEHICLES ONLY

See Figure 1

The Camshaft Position (CMP) sensor used in these engines is a three wire, Hall effect type sensor. The sensor requires power and ground to function. When performing this test, backprobe all connectors.

  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, alternating from 0-12 volts should be seen at terminal C. If the voltage is within specification, the sensor is functional
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Camshaft Position (CMP) sensor circuit - 1996 2.2L (VIN 4) engine

  1. If the sensor voltage is not within specifications, use a DVOM to check terminal A for battery positive (B+). If battery positive (B+) is not present, check the circuit continuity and repair as necessary.
  2.  
  3. If battery positive (B+) is present at terminal C, check terminal B 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.  

3.1L (VIN M) Engine

See Figure 2

  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, alternating from 0-12 volts should be seen at terminal B. If the voltage is within specification, the sensor is functional
  4.  



Click image to see an enlarged view

Fig. Fig. 2: Camshaft Position (CMP) sensor circuit - 3.1L (VIN M) engine

  1. If the sensor voltage is not within specifications, use a DVOM to check terminal A for battery positive (B+). If battery positive (B+) is not present, check the circuit continuity and repair as necessary.
  2.  
  3. If battery positive (B+) is present at terminal A, check terminal C 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



1996 2.2L (VIN 4) Engine

See Figure 3

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the CMP sensor harness connector.
  4.  
  5. Unfasten the CMP sensor bolt, then remove the sensor from the vehicle.
  6.  
  7. Inspect the sensor O-ring for wear, cracks or deterioration and replaced if necessary.
  8.  



Click image to see an enlarged view

Fig. Fig. 3: Exploded view of the CMP sensor mounting - 1996 2.2L engine

To install:
  1. Lubricate a new sensor O-ring with clean engine oil, then install on the sensor.
  2.  
  3. Install the CMP sensor and secure with the retaining bolt. Tighten the bolt to 6-9 ft. lbs. (9-12 Nm).
  4.  
  5. Attach the sensor harness connector.
  6.  
  7. Connect the negative battery cable.
  8.  

3.1L Engine

See Figures 4, 5 and 6

  1. Disconnect the negative battery cable.
  2.  
  3. Use a block of wood and a floor jack to properly support the engine oil pan.
  4.  
  5. Remove the right engine mount. It is secured with 5 bolts and 1 nut.
  6.  
  7. Remove the serpentine drive belt.
  8.  
  9. Remove the retaining nuts and bolt, then remove the alternator braces.
  10.  
  11. Unbolt the power steering pump, then position the pump aside. Do NOT disconnect the fluid lines.
  12.  
  13. Detach the CMP sensor electrical connector.
  14.  



Click image to see an enlarged view

Fig. Fig. 4: Exploded view of the CMP sensor and electrical harness - 1995 3.1L engine shown

Use special tool J 38125-A. This tool requires the removal of the plastic connector from the wires for clearance. Do NOT cut the electrical connector.

  1. Remove the retaining bolt, then remove the CMP sensor from the vehicle.
  2.  



Click image to see an enlarged view

Fig. Fig. 5: Location of the CMP sensor retaining bolt (see arrow)



Click image to see an enlarged view

Fig. Fig. 6: Remove the CMP sensor from the vehicle

To install:
  1. Install the CMP sensor. Reroute the electrical pigtail under the power steering pump and alternator pencil brace.
  2.  
  3. Install the alternator braces.
  4.  
  5. Install the serpentine drive belt.
  6.  
  7. Install the right engine mount, then connect the negative battery cable.
  8.  

 
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