GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Camshaft Position (CMP) Sensor

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OPERATION



The control module uses the camshaft position sensor to determine the position of the No. 1 piston during its power stroke. This signal is used to calculate the ignition and fuel injection timing. On most vehicles, if the camshaft position sensor signal is lost while the engine is running, the fuel injection system will shift to a calculated fuel injection mode and the engine will continue to run. However, once an attempt is made to restart the engine, the engine will not fire.

Only 2.4L and 3.1L engines use a camshaft position sensor.

TESTING



See Figures 2 and 1

Click image to see an enlarged view

Fig. Fig. 1: Attach suitable jumper wires between the CMP sensor and CMP sensor harness. Connect a DC volt meter to the jumper wires corresponding to IGN and sensor ground terminals and note the reading



Click image to see an enlarged view

Fig. Fig. 2: Connect the volt meter to the jumper wire corresponding to signal and sensor ground terminals, rotate the engine and observe the volt meter and verify that the voltage signal varies from approximately zero volts to slightly less than supply voltage

  1. Remove the PCM fuse to prevent the engine from starting. Removal of the PCM fuse does not disable the sensor power supply and allows testing of this sensor safely.
  2.  
  3. Disconnect the CMP sensor wiring harness and attach suitable jumper wires between the CMP sensor and CMP sensor harness. Connect a DC volt meter to the jumper wires corresponding to CMP IGN or PWR terminal and sensor ground.
  4.  
  5. With the ignition ON and the engine off, verify that the voltage is approximately battery voltage. The supply voltage should be slightly less than battery voltage.
  6.  

  1. If not as specified, repair or replace the fuse and/or wiring.
  2.  
  3. Connect a DC volt meter to the jumper wires corresponding to CMP signal terminal and sensor ground.
  4.  
  5. Place a socket and breaker bar or the crankshaft pulley bolt and rotate the engine slowly by hand. Observe the volt meter and verify that the voltage signal varies from approximately zero volts to slightly less than supply voltage. The voltage will switch on when the target passes the sensor and will show little or no voltage when the target is past the sensor.
  6.  
  7. If it is not as specified, the CMP sensor may be faulty.
  8.  

REMOVAL & INSTALLATION



2.4L Engine

See Figure 3

Click image to see an enlarged view

Fig. Fig. 3: The Camshaft Position (CMP) sensor-2.4L engines

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the sensor harness connector at the sensor.
  4.  
  5. Unfasten the retaining bolt, then remove the sensor from the camshaft housing.
  6.  

To install:
  1. Place the sensor into position.
  2.  
  3. Install the CMP sensor retaining bolt, then tighten to 88 inch lbs. (10 Nm).
  4.  
  5. Attach the sensor harness connector.
  6.  
  7. Connect the negative battery cable.
  8.  

3.1L Engine

See Figure 4



Click image to see an enlarged view

Fig. Fig. 4: View of the factory routing of the CMP sensor. When installing the sensor, be careful not to damage the wire pigtail

  1. Disconnect the negative battery cable.
  2.  
  3. Support the engine by the oil pan.
  4.  
  5. Unfasten the 5 bolts and one nut securing the right engine mount, then remove the mount from the vehicle.
  6.  
  7. Remove the serpentine belt.
  8.  
  9. Remove the 3 nuts and one bolt retaining the alternator braces, then remove the braces.
  10.  
  11. Keeping the fluid lines attached, unfasten the 3 power steering pump retaining bolts, then remove the pump.
  12.  
  13. Using special tool J-38125-A or equivalent, remove the camshaft position sensor. It is retained by one bolt and an electrical connector. The special tool requires the removal of the plastic connector from the wires for clearance. Do NOT cut the pigtail!
  14.  

To install:
  1. Install the camshaft position sensor. Re-route the pigtail under the power steering pump and alternator brace. Make sure to route the pigtail away from electronic components to avoid Electromagnetic Interference (EMI).
  2.  
  3. Install the power steering pump assembly, then the alternator braces.
  4.  
  5. Install the serpentine drive belt, then the right engine mount.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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