Engine Speed Signal
The TCM uses a direct signal from distributor pick-up coil or crankshaft position sensor to determine engine RPM. The TCM uses the direct signal and compares it to the engine speed received from the Powertrain Control Module (PCM) by the CCD bus to confirm that direct engine speed signal is valid.
NOTE:
The TCM uses a direct engine speed signal instead of using CCD bus signal to avoid any time delay that may occur when CCD bus circuit is used.