Silverado 2008

Camshaft Position (CMP) Sensor

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Location



Specific to:

Chevrolet Silverado 1500 2008

The Camshaft Position (CMP) is located above the crankshaft pulley.

Operation



Specific to:

Chevrolet Silverado 1500 2008

The Camshaft Position (CMP) Sensor is a permanent magnet output coil device that operates within a 5 volt DC reference range, and monitors the speed and position of the camshaft. A reluctor is attached directly to the camshaft, and is used to generate a digital signal as it passes the magnetic coil; the alternating lines of magnetic flux are used by the sensor to produce a digital pulse. The CMP signal is used by the Powertrain Control Module (PCM) to calculate ignition timing, firing order, fuel injector timing, and misfire diagnostics.

Testing



Specific to:

Chevrolet Silverado 1500 2008


NOTE
Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

CMP Circuit Testing

Specific to:

Chevrolet Silverado 1500 2008

Use a suitable scan tool or a Graphing Multi-Meter (GMM in order to view the CMP data.

CMP Sensor logic is based on alternating lines of magnetic flux which generate a digital ON/OFF signal to the PCM, and are based on the speed and position of the camshaft.

Verify that the engine timing components (timing belt, timing chain, or timing gears) are properly installed, and that there is no foreign material obstructing the path between the reluctor and the CMP sensor. If any engine mechanical faults are evident, locate and repair as required before continuing.

A Digital Volt-Ohm Meter (DVOM) may be used to verify the condition of the wiring: additional information may be acquired by taking measurements at the sensor connector as well as the PCM connector. If significant resistance is measured (greater than 5 ohms) is measured, check the wiring harness and connections for corrosion, poor pin connections, or damaged wires.

If all engine wiring and pin connections are confirmed, disconnect the CMP Sensor to verify the signal with a GMM, and verify PCM communication before replacing the CMP Sensor.

Click image to see an enlarged view

Fig. CMP Sensor Range Chart

CMP Sensor Strategy

Specific to:

Chevrolet Silverado 1500 2008

The CMP Sensor provides a digital input signal (See Figure 1) to the Powertrain Control Module (PCM) for a number of engine control system calculations. The CMP signal is compared with the Crankshaft Position Sensor (CKP) and Vehicle Speed Sensor (VSS) for measured operating conditions, and the Pulse Width Modulation pattern is used by the Powertrain Control Module (PCM) to calculate ignition timing, firing order, fuel injector timing, and misfire diagnostics.

CMP Sensor feedback patterns vary according to the reluctor configuration and PCM logic. While most models use a single tooth for Top Dead Center (TDC), others may use multiple reluctor teeth for additional positions of camshaft rotation, which may include one per cylinder, or 0°,90°, 180°, and 270° respectively.

Connection And Wiring Diagnosis

Specific to:

Chevrolet Silverado 1500 2008

Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

Many intermittent open or short circuits may be caused by wiring harness and connector movement due to vibration, engine torque, bumps and rough pavement, etc.

  1. Test the wiring harness and connectors by performing the following tests:

    Move the related connectors and wiring while monitoring the appropriate scan tool data.
     
    Move the related connectors and wiring with the component commanded ON and OFF. Using a suitable the scan tool, observe the component operation.
     
    With the engine running, move the related connectors and wiring while monitoring component operation.
     
    If harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary.
     

  2.  
  3. Test the connector terminal pins and/or wiring by performing the following tests:

    Inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body.
     
    Inspect for improperly formed or damaged terminals and test for incorrect terminal tension.
     
    Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
     
    Inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and/or brittle sections of wire in the suspect circuits.
     
    Inspect for wires that are broken inside the insulation by gently pulling on suspect sections of wiring.
     

  4.  

Related Diagnostic Trouble Codes

Specific to:

Chevrolet Silverado 1500 2008



Click image to see an enlarged view

Fig. Related Diagnostic Trouble Codes

Removal & Installation



4.3L Engines

Specific to:

Chevrolet Silverado 1500 2008

  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Unplug the harness connector from the CMP sensor.
  6.  
  7. Unplug the harness connector from the CMP sensor.
  8.  
  9. Remove the water pump.
  10.  
  11. Remove the CMP sensor bolt, then remove the sensor from the engine.

    Click image to see an enlarged view

    Fig. CMP sensor mounting-4.3L engines

  12.  

To install:


NOTE
Be sure to use new fasteners, as required.

  1. Installation is the reverse of removal.
  2.  
  3. Lubricate a new O-ring with clean engine oil. Tighten the bolt to 89 inch lbs. (10 Nm).
  4.  

4.8L, 5.3L & 6.0L Engines

Specific to:

Chevrolet Silverado 1500 2008

  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Raise and support the vehicle safely.
  6.  
  7. Unplug the harness connector from the CMP sensor.
  8.  
  9. Remove the CMP sensor harness bolts, then remove the sensor from the engine.

    Click image to see an enlarged view

    Fig. CMP sensor harness mounting (type one)-4.8L, 5.3L & 6.0L engines



    Click image to see an enlarged view

    Fig. CMP sensor harness mounting (type two)-4.8L, 5.3L & 6.0L engines

  10.  

To install:


NOTE
Be sure to use new fasteners, as required.

  1. Installation is the reverse of removal.
  2.  
  3. Lubricate a new O-ring with clean engine oil. Tighten the bolt to 106 inch lbs. (12 Nm).
  4.  

 
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