Theory Of Operation
The Powertrain Control Module (PCM) uses the Crankshaft Position (CKP) Sensor signal and the Camshaft Position (CMP) Sensor signal together to identify engine timing/firing order. This process is done by recognizing the patterns of each signal. From those patterns an engine position can be determined. This process is described as engine synchronization.
- The CKP Sensor contains an Integrated Circuit (IC) and a magnet. The sensor outputs a digital signal based on the magnetic flux changes of the magnet created from the teeth and valleys of the tone wheel located on the Crankshaft or Flex Plate depending on engine. The PCM identifies the Crankshaft position angle by recognizing the reference tooth/gap. The reference tooth or gap is the largest feature of the tone wheel. This identification process is said to "lock" the crank signal.
- The PCM determines the Camshaft position angle in a similar way. By recognizing unique but successive features on the Camshaft tone wheel, the PCM can identify the particular angle at which the camshaft signal is indicating. Upon recognition of the Camshaft signal pattern sequence, it is also said to be "locked".
When both locked conditions have been met, the engine is said to be synchronized. At this time, sequencing the ignition timing and fuel injection events for the engine can begin. From the CKP signal, engine speed and misfire detection are also determined. When the PCM loses pattern recognition of the CKP signal, it is said to be "unlocked". The PCM will try to re-establish pattern recognition. If the PCM fails to achieve the pattern recognition, or if the CKP Signal unlocks more than a calibrated number of times within a calibrated threshold of time, a code is set.
The engine may still start even if either the CKP or CMP fails. The PCM eventually sorts out engine position and can start the vehicle on just one of these two inputs. However, there is a delay in starting until the PCM can establish sync. A DTC is set and the MIL illuminates if either of the CKP or CMP Sensor signals are not present during engine cranking.