Theory Of Operation

For proper engine control and combustion stability the Camshaft (CMP) and Crankshaft (CKP) positions must be aligned and known so that fuel injection and spark timing can be introduced at the intended Piston and Intake/Exhaust Valve positions. During vehicle manufacturing, at end of line, or if a Cam/Crank Relearn is performed, the system learns the difference between the Camshaft and Crankshaft position in terms of engine degrees and stores it in the EEPROM. During every following driving cycle, the Powertrain Control Module (PCM) uses this value to compare.

Within a driving cycle, once the CMP position and CKP position are known and verified they are considered "locked." This diagnostic will only run when both sensor signals are in the "locked" state. Engine position is constantly tracked as the CMP Sensor and CKP Sensor signals are monitored by the PCM. An engine rotating at a constant speed would produce engine signals that match the nominal pattern exactly. With engine acceleration and deceleration the engine signals are compressed or stretched in time relative to nominal timing. The PCM takes into account and adjusts for any acceleration/deceleration rates that are in effect.

The misalignment fault accounts for angular deviation between the CMP Sensor and CKP Sensor signals due to miss builds, chain stretch, or a skipped tooth. This fault results from the difference between the positions indicated by the CMP Sensor and CKP Sensor signals. The result is only valid if both positions are "locked".