Engine Speed Signal
PCM sends an engine speed signal to TCM across CCD or PCI bus. TCM does not receive a direct input from CKP sensor. TCM uses direct signal and compares it to engine speed received from PCM by CCD or PCI bus to confirm direct engine speed signal is valid.
NOTE:
TCM uses a direct engine speed signal instead of using bus signal to avoid any time delay that may occur when bus circuit is used.