Camshaft Position (CMP) Actuator Diagnosis

The camshaft position actuator will only phase 25-cam degrees retard (counterclockwise). Full advance (clockwise) is 0 degrees. The arrow on the actuator shows advance direction.

Fig 1: Rotating Exhaust Camshaft And Camshaft Position Actuator Back And Forth

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The camshaft position actuator should always be serviced/replaced in the full advanced position (full clockwise or 0 degrees). New replacement (service) camshaft position actuators are shipped at full advance or 0 degrees. To be sure the camshaft position actuator is performing properly, perform the following to help in the diagnostics.

1. Use a 25 mm (1 in) wrench on the hex of the exhaust camshaft to rotate the exhaust camshaft and camshaft position actuator back and forth (clockwise and counterclockwise) to purge the oil out of the camshaft position actuator.
   Fig 2: Drawing Line Flush With Head On Camshaft Position Actuator

   Courtesy of GENERAL MOTORS CORP.
2. To perform an on-vehicle test, scribe or draw a line (1) on the camshaft position actuator, flush with the head, in the full advanced position. See arrow on the camshaft position actuator. With the engine at TDC on #1 cylinder, the wording should be level.
3. Use a 25 mm (1 in) wrench on the hex of the exhaust camshaft to rotate the camshaft and camshaft position actuator counterclockwise to full retard.
   Fig 3: Drawing Line On Camshaft Position Actuator

   Courtesy of GENERAL MOTORS CORP.
4. Scribe or draw a line (2) on the camshaft position actuator at that position.
   Fig 4: Measuring Distance Between Two Lines

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5. Measure the distance between the two lines. The measurement (3) should be 14-15 mm (0.55-0.59 in). If the measurement is far more or far less, the camshaft position actuator needs to be replaced.