P0740

P0740 means the TCM has detected an electrical fault in the Torque Converter Clutch (TCC) solenoid circuit — open, shorted, or out-of-range resistance on the solenoid that controls converter lockup. This is a 'circuit' code, not a 'performance' code (that's P0741) — meaning the TCM can't even verify the solenoid is electrically there. Start with the fluid check and condition, then go straight to the external harness at the transmission case connector: P0740 is one of the highest-rate connector-corrosion false-positives in the diagnostic catalog. Unplug the case connector, inspect for green corrosion or pin pushback, dielectric-grease everything, clear the code, and road-test. If the code returns, the next step is a resistance check across the TCC solenoid pins at the case connector — most TCC solenoids spec between 10-30 ohms (verify with FSM). Out-of-spec resistance is a solenoid swap; in-spec resistance points to wiring upstream toward the TCM. The solenoid itself is almost always replaced as part of a solenoid pack on modern trans, not individually.

Vehicle-specific patterns: 2002-2007 Honda Accord/Odyssey 5AT throws P0740 from a known TCC solenoid failure — Honda part number 28250-P7W-003, $40-80 part, accessible externally without dropping the pan, 30-minute job. 2004-2010 Ford Mustang/F-150 with the 4R70W/4R75E throws P0740 from harness corrosion at the case pass-through connector far more often than from an actual solenoid failure — 80% of these codes resolve with connector cleanup and dielectric grease per Ford TSB 06-14-4. 2003-2009 Toyota 4Runner/Tundra with the A750E/A750F throws P0740 from a degraded TCC solenoid that's accessible after pan drop — $80 solenoid plus pan gasket. 2005-2010 GM Silverado/Tahoe with the 4L60E throws P0740 from internal harness chafing at the case pass-through OR a failed TCC PWM solenoid in the valve body — pan drop required either way. Estimated repair: $150 (connector cleanup) to $600 (solenoid + pan service).