- Crankshaft sensor is responsible for PIP (profile ignition pickup).
- Camshaft sensor sends CID (cylinder identification) to DIS.
- DIS delivers signal to EEC.
A signal goes from the EEC to the VMM (Vehicle Maintenance/Measurement/Management Module) and then to the tach.
-=-=-=-
When a valid CID signal is lost from the camshaft sensor, the DIS and EEC both switch to FMEM (Failure Management Effects Mode).
During FMEM, the DIS handles injector firing and the EEC handles CID, each 'guessing' as to which cylinder needs fuel and spark. FMEM cuts output to the VMM and thus, no tach. Note that the VMM will go dark after 15 minutes without a signal. The tach 'bounces' when the signal is suddenly dropped/activated as FMEM, in this case, comes and goes based on the EEC's attempts to reestablish a connection with the camshaft sensor.