Crankshaft and Camshaft Synchronisation The crankshaft and camshaft must be synchronised for the engine to start. The CKP sensor registers the crankshaft position. The ECM calculates from the signal the TDC positions (exhaust or injection TDC). The ECM uses the CMP sensor signal to determine which TDC position relates to exhaust or injection. The ECM compares the two signals to provide the correct injector sequence. The injector sequence is then repeated corresponding to the engine firing order If a valid signal from the CMP sensor is not received after two full engine revolutions, fuel injection is terminated and the engine will not start.