Camshaft Position Sensor

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The Camshaft Position (CMP) sensor works in conjunction with a 1X reluctor wheel on the camshaft. The PCM provides a 12 volt reference to the CMP sensor as well as a low reference and a signal circuit. As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads. CMP sensor is mounted on timing chain cover. See Fig 1 .

The CMP sensor 1X signal is used by the PCM to determine if the cylinder at Top Dead Center (TDC) is on the firing stroke or exhaust stroke. The PCM can determine TDC for all cylinders by using the CKP sensor 24X signal alone. The engine will start without a CMP signal as long as the PCM receives the CKP sensor 24X signal. A slightly longer cranking time may be a symptom of this condition. The system attempts synchronization and looks for an increase in engine speed indicating that the engine started. If PCM does not detect an increase in engine speed, PCM assumes that the PCM incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. If PCM detects that a CMP to CKP mis-match has occurred a DTC will set.

Fig 1: Locating Camshaft Position & Knock Sensors

Courtesy of GENERAL MOTORS CORP.