Transmission Control Switch (TCS) Or Transmission Control Indicator Lamp (TCIL) Circuit Malfunction

DTC P1780 DETECTION CONDITION AND POSSIBLE CAUSE

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 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, the PCM illuminates the transmission control indicator lamp (TCIL) 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.

DTC P1780 INSPECTION

STEP	INSPECTION		ACTION
1	Was PCM Quick Test performed?	Yes	Go to next step.
		No	Perform PCM Quick Test.
2	CHECK TEST VALIDITY Key ON, Engine OFF (KOEO). Access the TCS PID using NGS Tester. Cycle the TCS switch button, then hold it depressed. Does TCS PID reading switch from ON to OFF, and does reading indicate ON when button is depressed?	Yes	Rerun KOER Self Test to cycle TCS.
		No	Go to next step.
3	CHECK TRANSMISSION CONTROL SWITCH (TCS) CIRCUIT FOR VOLTAGE Key OFF. Disconnect PCM. Install Breakout Box, leave PCM disconnected Key ON, Engine OFF (KOEO). Measure voltage between PCM test pin 29 (TCS) and PCM test pins 24 and 77 (PWR GND) while cycling the TCS several times. Does voltage cycle?	Yes	Replace PCM. See COMPUTERIZED ENGINE CONTROLS . Go to step 7.
		No	Go to next step.
4	CHECK HARNESS CIRCUIT(S) FOR SHORT TO GROUND Key OFF. Disconnect TCS. Measure resistance between PCM test pin 29 (TCS) and PCM test pins 24 and 77 (PWR GND). Is resistance greater than 10K ohms?	Yes	Go to next step.
		No	Repair short circuit. Go to step 7.
5	CHECK RESISTANCE OF THE TCS HARNESS Measure resistance of TCS circuit between I/P fuse panel fuse 27 (15A) and TCS harness connector. Measure resistance of TCS circuit between PCM test pin 29 and TCS harness connector. Is each resistances less than 5.0 ohms?	Yes	Go to next step.
		No	Repair open circuit. Go to step 7.
6	CHECK HARNESS CIRCUIT FOR SHORTS TO POWER Measure resistance between PCM test pin 29 (TCS) and PCM test pins 71 and 97 (VPWR). Is resistance greater than 10K ohms?	Yes	Replace damaged Transmission Control Switch, Go to step 7.
		No	Repair short circuit. Go to step 7.
7	VERIFY TROUBLESHOOTING OF DTCs COMPLETED Make sure to reconnect all disconnected connectors. Clear DTCs from PCM memory using NGS tester generic OBD-II function. Perform PCM Quick Test. Is same DTC present?	Yes	Replace PCM. See COMPUTERIZED ENGINE CONTROLS . Repeat PCM QUICK TEST .
		No	If any other DTC is present, go to applicable DTC inspection. If no DTC is present, troubleshooting complete.