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

DTC P1780 DETECTION CONDITION & 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.

DTC P1780 DIAGNOSTIC PROCEDURE

DTC P1780		TRANSMISSION CONTROL SWITCH (TCS) OR TRANSMISSION CONTROL INDICATOR LAMP (TCIL) CIRCUIT MALFUNCTION
STEP	INSPECTION		ACTION
1	Was the PCM quick test performed?	Yes	Go to next step.
1	Was the PCM quick test performed?	No	Perform PCM quick test. See PCM QUICK TEST .
2	CHECK TEST VALIDITY Key on, engine off (KOEO). Using WDS or equivalent tester, select Diagnostic Data Link. Select PCM. Select PID/Data Monitor and Record. Access the TCS PID. 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.
2		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 POWERTRAIN CONTROL MODULE (PCM) REMOVAL / INSTALLATION . Go to step 7.
3		No	Go to next step.
4	CHECK HARNESS CIRCUIT(S) FOR SHORT TO GROUND Key OFF. Disconnect TCS. Measure the resistance between PCM test pin 29 (TCS) and PCM test pins 24 and 77 (PWR GND). Is the resistance greater than 10K ohms?	Yes	Go to next step.
4		No	Repair short circuit. Go to step 7.
5	CHECK RESISTANCE OF THE TCS HARNESS Measure resistance of TCS circuit between smart junction box fuse 20 (10A) and TCS harness connector. Measure resistance of TCS circuit between PCM test pin 29 and TCS harness connector. Is each resistance less than 5.0 ohms?	Yes	Go to next step.
5		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 the resistance greater than 10K ohms?	Yes	Replace damaged TCS. See TRANSMISSION CONTROL SWITCH (TCS) REMOVAL / INSTALLATION . Go to next step.
6		No	Repair short circuit. Go to next step.
7	VERIFY TROUBLESHOOTING OF DTCs COMPLETED Connect all disconnected connectors. Clear DTCs from PCM memory using WDS or equivalent tester. Perform PCM quick test. Is same DTC present?	Yes	Replace PCM. See POWERTRAIN CONTROL MODULE (PCM) REMOVAL / INSTALLATION . Repeat PCM quick test.
7		No	In any other DTC is present, go to applicable DTC inspection. See DIAGNOSTIC TROUBLE CODE (DTC) INDEX - POWERTRAIN CONTROL MODULE (PCM) . If no DTC is present, troubleshooting is complete.