Malibu, Malibu MAXX 2006-2008

Camshaft Position Sensor

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Description & Operation



The Camshaft Position (CMP) sensor is triggered by a notched reluctor wheel built onto the camshaft sprocket. The CMP sensor provides four signal pulses every camshaft revolution. Each notch, or feature of the reluctor wheel is of a different size which is used to identify the compression stroke of each cylinder and to enable sequential fuel injection. The ECM uses the CMP sensor output signal to determine the camshaft relative position to the crankshaft position.

The CMP sensor is connected to the Engine Control Module (ECM) by the following circuits:



A 5-volt reference circuit
 
A low reference circuit
 
A signal circuit
 

The 4X Camshaft Position (CMP) sensor circuits consist of an Engine Control Module (ECM) supplied 5-volt reference circuit, low reference circuit, and an output signal circuit. The CMP sensor is an internally magnetic biased digital output integrated circuit sensing device. The sensor detects magnetic flux changes of the teeth and slots of a 4-tooth reluctor wheel attached to the camshaft. As each reluctor wheel tooth rotates past the CMP sensor, the resulting change in the magnetic field is used by the sensor electronics to produce a digital output pulse. The sensor returns a digital ON/OFF DC voltage pulse of varying frequency, with 4 varying width output pulses per camshaft revolution that represent an image of the camshaft reluctor wheel. The frequency of the CMP sensor output depends on the velocity of the camshaft. The ECM decodes the narrow and wide tooth pattern to identify camshaft position. This information is then used to determine the optimum ignition and injection points of the engine. The ECM also uses the CMP sensor output information to determine the camshaft relative position to the crankshaft, to control camshaft phasing, and for limp-home operation.

Removal & Installation



2.2L (L61) Engine
  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Disconnect the engine wiring harness electrical connector from the intake Camshaft Position (CMP) sensor.
  4.  
  5. Remove the CMP sensor bolt.
  6.  
  7. Remove the CMP sensor.
  8.  

To install:


NOTE
Inspect the CMP sensor for damage, replace as necessary.

  1. Lubricate the CMP sensor O-ring seal with clean engine oil.
  2.  
  3. Install the CMP sensor.
  4.  
  5. Install the CMP sensor bolt.
  6.  
  7. Tighten the CMP sensor bolt to 89 inch. lbs. (10 Nm).
  8.  
  9. Connect the engine wiring harness electrical connector (1) to the intake CMP sensor.
  10.  

3.5L (LZ4) Engine
  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Remove the intake manifold cover. if required.
  4.  
  5. Remove the power steering pump, if required.
  6.  
  7. Disconnect the fuel injector wiring harness electrical connector from the camshaft position (CMP) sensor.
  8.  
  9. Remove the CMP sensor bolt.
  10.  
  11. Remove the CMP sensor.
  12.  
  13. Inspect the sensor O-ring for wear, cracks, or leakage if the sensor is not being replaced.
  14.  

To install:

  1. Replace the O-ring if damaged, lubricate the NEW O-ring with clean engine oil.
  2.  
  3. Install the CMP sensor.
  4.  
  5. Install the CMP sensor bolt.
  6.  
  7. Tighten the CMP sensor bolts to 89 inch. lbs. (10 Nm).
  8.  
  9. Connect the fuel injector wiring harness electrical connector to the CMP sensor.
  10.  
  11. Install the power steering pump, if required.
  12.  
  13. Install the intake manifold cover. if required.
  14.  

3.9L (LZ9) Engine
  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Remove the power steering pump
  4.  
  5. Disconnect the camshaft position (CMP) sensor electrical connector.
  6.  
  7. Remove the CMP sensor bolt.
  8.  
  9. Remove the CMP sensor.
  10.  
  11. Inspect the sensor O-ring for wear, cracks, or leakage if the sensor is not being replaced.
  12.  

To install:

  1. Replace the O-ring if damaged, lubricate the NEW O-ring with clean engine oil.
  2.  
  3. Install the CMP sensor.
  4.  
  5. Install the CMP sensor bolt.
  6.  
  7. Tighten the CMP sensor bolts to 89 inch. lbs. (10 Nm).
  8.  
  9. Connect the CMP sensor electrical connector.
  10.  
  11. Install the power steering pump.
  12.  

Testing



Test the Camshaft Position (CMP) sensor circuit as follows:

  1. Ignition OFF, disconnect the appropriate CMP sensor wire harness connector.
  2.  
  3. Test for less than 1 ohm of resistance between the low reference circuit terminal B and ground.
  4.  
  5. If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM
  6.  
  7. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal A and ground.
  8.  
  9. If less than the specified range, test the 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM
  10.  
  11. If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  12.  
  13. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal C and ground.
  14.  
  15. If less than the specified range, test the signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
  16.  
  17. If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  18.  
  19. Ignition OFF, connect a fused jumper wire to the CMP signal circuit terminal C.
  20.  
  21. Ignition ON, momentarily touch the other end of the fused jumper wire to the battery negative post. The CMP active counter parameter on the scan tool should increment.
  22.  
  23. If the CMP active counter increments, replace the CMP sensor.
  24.  
  25. If the CMP active counter does not increment, replace the ECM.

    Click image to see an enlarged view

    Fig. 3.5L (LZ4) Camshaft Position (CMP) sensor electrical connector view



    Click image to see an enlarged view

    Fig. 3.9L (LZ9) Camshaft Position (CMP) sensor electrical connector view

  26.  

Test the Camshaft Position (CMP) sensor as follows:

  1. Inspect the Camshaft Position (CMP) sensor for correct installation. Remove the CMP sensor from the engine and inspect the sensor and the O-ring for damage.
  2.  
  3. If the sensor is loose, incorrectly installed, or damaged, repair or replace the CMP sensor.
  4.  
  5. Connect the CMP sensor connector to the CMP sensor. Turn ON the ignition, with the engine OFF.
  6.  
  7. Ignition ON, and engine OFF. Observe the CMP Active Counter parameter on the scan tool. Pass a steel object by the tip of the sensor repeatedly. The CMP Active Counter parameter should increment.
  8.  
  9. If the parameter does not increment, replace the CMP sensor.
  10.  

 
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