GM Full-Size Trucks 1988-1998 Repair Information

Camshaft Position (CMP) Sensor

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OPERATION



See Figure 1

The ECM uses the camshaft signal to determine the position of the No. 1 cylinder piston during its power stroke. The signal is used by the ECM 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.



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Fig. Fig. 1: Camshaft Position (CMP) sensor location

TESTING



See Figure 2



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Fig. Fig. 2: Camshaft Position (CMP) sensor wiring schematic

  1. Disconnect the CMP sensor wiring harness and connect an LED test light between CMP harness terminal C and battery ground.
  2.  
  3. With the ignition ON and the engine off, verify that the test light illuminates.
  4.  
  5. If not as specified, repair or replace the fuse and/or wiring.
  6.  
  7. Carefully connect the test light between CMP harness terminal A and C and verify that the test light illuminates.
  8.  
  9. If not as specified, repair the CMP harness ground circuit (terminal A).
  10.  
  11. Turn the ignition OFF and disconnect the test light.
  12.  
  13. Next, connect suitable jumper wires between the CMP sensor and CMP sensor harness. Connect a DC volt meter to the jumper wire corresponding to CMP terminal B and battery ground.
  14.  
  15. Start the engine and verify that the voltage signal is 5-7 volts.
  16.  
  17. If it is not as specified, the CMP sensor may be faulty.
  18.  

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Detach the sensor harness connector at the sensor.
  4.  
  5. Unfasten the retaining bolt, then remove the sensor from the camshaft housing. Inspect the sensor O-ring for wear, cracks or leakage and replace if necessary.
  6.  

To install:
  1. Lubricate the O-ring with clean engine oil, then place on the sensor. Install the sensor into the camshaft housing.
  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.  

 
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