GM Camaro/Firebird 1993-1998 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.

3.4L Engine

See Figure 1

  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. 1: Camshaft Position (CMP) sensor circuit-3.4L 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.  

3.8L 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 A. 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-3.8L engine

  1. If the sensor voltage is not within specifications, use a DVOM to check terminal C 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.  

REMOVAL & INSTALLATION



3.4L Engine
1993 VEHICLES

The camshaft position sensor is located on top of the engine block, behind the water pump, near the lower intake manifold assembly.

  1. Be sure the ignition is in the OFF or LOCK position, then disconnect the negative battery cable.
  2.  
  3. Disengage the wiring harness connector from the sensor.
  4.  
  5. Remove the sensor retaining bolt, then carefully remove the sensor from the top of the engine block. If necessary, use a small flat-bladed tool to carefully pry between alternate sides of the sensor and the engine block in order to loosen the sensor from its mounting boss. Make sure the sensor is not damaged when prying.
  6.  

To install:
  1. Inspect the sensor O-ring and replace, if necessary.
  2.  
  3. Lubricate the O-ring with clean engine oil, then install the sensor into the engine block.
  4.  
  5. Install the sensor retaining bolt and tighten to 17 inch lbs. (1.9 Nm).
  6.  
  7. Engage the sensor wiring harness, then connect the negative battery cable.
  8.  

1994-95 VEHICLES

See Figure 3

  1. Be sure the ignition is in the OFF or LOCK position, then disconnect the negative battery cable.
  2.  
  3. Remove the throttle cable shield and bracket from the throttle body.
  4.  
  5. Disengage the wiring harness connector from the sensor.
  6.  
  7. Remove the sensor retaining bolt, then carefully remove the sensor from the engine.
  8.  



Click image to see an enlarged view

Fig. Fig. 3: Camshaft position sensor-1994 3.4L engine

To install:
  1. Inspect the sensor O-ring and replace, if necessary.
  2.  
  3. Lubricate the O-ring with clean engine oil, then install the sensor into the engine block.
  4.  
  5. Install the sensor retaining bolt and tighten to 8 ft. lbs. (10 Nm).
  6.  
  7. Engage the sensor wiring harness.
  8.  
  9. Install the throttle cable bracket and shield.
  10.  
  11. Connect the negative battery cable.
  12.  

3.8L Engine

See Figures 4 and 5

  1. Be sure the ignition is in the OFF or LOCK position, then disconnect the negative battery cable.
  2.  



Click image to see an enlarged view

Fig. Fig. 4: Camshaft Position (CMP) sensor location (see arrow)-3.8L engine

  1. Detach the electrical connector from the camshaft position sensor.
  2.  
  3. Remove the camshaft position sensor bolt/screw.
  4.  
  5. Remove the camshaft position sensor from the engine front cover. If necessary, use a small flat-bladed tool to carefully pry between the sensor and the front cover from alternate sides to loosen the sensor from its mounting position. Be careful not to damage the sensor or mounting flange.
  6.  
  7. Inspect the sensor O-ring for wear, cracks and/or damage and replace, if necessary.
  8.  



Click image to see an enlarged view

Fig. Fig. 5: On the 3.8L engine, the camshaft position sensor is mounted to the front cover

To install:
  1. Lubricate the sensor O-ring seal with clean engine oil.
  2.  
  3. Position the sensor to the front cover and secure with the retaining bolt/screw. Tighten the bolt/screw to 89 inch lbs. (10 Nm).
  4.  
  5. Attach the sensor electrical connector, then connect the negative battery cable.
  6.  

5.7L Engine

See Figure 6

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the intake manifold.
  4.  
  5. Detach the CMP sensor electrical connector.
  6.  
  7. Clean the area around the CMP sensor to avoid getting debris in the engine.
  8.  
  9. Remove the CMP sensor retaining bolt, then remove the sensor from the engine.
  10.  



Click image to see an enlarged view

Fig. Fig. 6: You must remove the intake manifold to access the CMP sensor on the 5.7L engine

To install:
  1. Install the CMP sensor and retaining bolt. Tighten the bolt to 18 ft. lbs. (25 Nm).
  2.  
  3. Attach the CMP sensor electrical connector.
  4.  
  5. Install the intake manifold.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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