Camshaft Position (CMP) Actuator System


1. The Camshaft Position (CMP) Actuator System is an electro-hydraulic system that changes the angle, or timing, of the camshaft relative to the crankshaft position. By controlling this, the CMP actuator system reduces emissions by using exhaust gases to help dilute the intake charge, broadens the engine torque range and increases fuel mileage.

2. The CMP actuator system consists of the Powertrain Control Module (PCM), the CMP actuator solenoid and the camshaft position actuator. The PCM controls the amount of oil that flows through an oil passage to the CMP actuator by sending a pulse-width-modulated signal to the CMP actuator solenoid. The oil flows through two passages; one passage is for advancing the camshaft and one passage is for retarding the cam. The CMP actuator is on the front end of the camshaft. When oil is directed by the solenoid through one passage, the variable cam sprocket advances the camshaft timing; when oil is directed through the other passage, the sprocket retards cam timing.

3. Any of the following factors can affect the operation of the CMP Actuator System:

a) Aftermarket oil additives
b) Incorrect engine oil level
c) Incorrect engine oil pressure
d) Incorrect engine oil temperature
e) Incorrect engine oil viscosity

Component replacement

Camshaft Position (CMP) actuator magnet

Warning: Wait until the engine is completely cool before beginning this procedure.

Note: The CMP actuator magnet is located on the timing chain cover above the balancer, on the front of the camshaft.

4. On 6.0L models, drain the cooling system (see Tune-up and routine maintenance), then remove the water pump (see Cooling, heating and air conditioning systems).

5. On non-6.0L models, remove the drive- belt and idler pulley (see Drivebelt check and replacement).

6. Disconnect the electrical connector from the CMP actuator magnet (see illustration).

18.6 CMP actuator magnet details (coolant crossover pipe removed for clarity)

1 Electrical connector
2 Mounting bolts

Chevrolet Silverado Emissions and engine control systems _ CMP actuator magnet details (coolant crossover pipe removed for clarity)

7. Remove the three CMP actuator magnet mounting bolts and remove the magnet.

8. Remove and discard the old CMP actuator magnet gasket.

9. Make sure that the gasket surface is clean and free of all debris.

10. Installation is the reverse of removal. Be sure to use a new gasket and tighten the CMP actuator magnet mounting bolts securely.

11. On 6.0L models, refill the cooling system (see Tune-up and routine maintenance).

Camshaft Position (CMP) actuator/ solenoid valve

12. See the CMP actuator/solenoid valve removal and installation procedure.

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