Mounted to the block below No. four injector, with the sensor tip close to the back of the flywheel. It has a light blue connector.
The CAS is an inductive probe, which generates an electrical impulse when cut outs in the flywheel pass the sensor tip.
Basically there are two functions 1. Engine speed. 2. crankshaft angle. Absolute key to the ECU management system. On cranking the ECU looks for pulses from the CAS before it switches on the fuel pump (after the ignition on priming routine). There are two “Gaps” in the series of holes otherwise cut at 10° intervals, these are reference points for the ECU to determine the crank shaft angle to time the ignition and injection. For a typical output waveform look here. On VVC models where the injection is sequential, the ECU also reads the cam phase .