Transmission Control Switch (TCS) Or Transmission Control Indicator Lamp (TCIL) Circuit Diagnosis (DTC P1780): Notes

DTC P1780 DETECTION CONDITION AND POSSIBLE CAUSES

DTC P1780	TRANSMISSION CONTROL SWITCH (TCS) OR TRANSMISSION CONTROL INDICATOR LAMP (TCIL) CIRCUIT MALFUNCTION
DETECTION CONDITION	P1780 indicates the TCS was not cycled during KOER self-test.
POSSIBLE CAUSE	Open or short circuit Damaged TCS Damaged powertrain control module (PCM) Damaged indicator bulb and/or fuse
HINT	TCS Description  Momentary contact switch that allows the driver to cancel overdrive gear. When TCS is pressed, a signal is sent to the PCM which then uses the shift solenoids to disengage/disable overdrive gear operation. At the same time, TCIL is illuminated to notify the driver that overdrive gear is canceled. When TCS is pressed again, overdrive gear operation is enabled and the TCIL is turned OFF. Whenever the ignition is cycled off and then on, the TCS is turned off and overdrive gear is enabled, even if the TCS had been on when ignition was shut off.
Courtesy of MAZDA MOTORS CORP.