P0740: Torque Converter Clutch Circuit/Open

What does P0740 mean?

The torque converter clutch (lock-up) connects pump and turbine mechanically; a solenoid – on/off, pulse-width modulated or proportional – moves a control valve in the valve body. Slip is engine speed minus turbine speed. Manufacturers do not use P0740–P0744 uniformly: Ford uses P0740 for open, P0742 for short to ground and P0744 for short to power, and reports stuck on as P2758. P0740 concerns the control circuit of the converter clutch solenoid. Ford flags an open circuit when the driver feedback line disagrees with the command for 0.5–5 s, with MIL; a 2006 GM table checks 0/12 V with more than 43 of 50 failed counts after two trips – newer GM units use P2761/P2763/P2764. FCA's Ram 6.7 reads P0740 as converter slip out of range and moved it to two trips by software in 2013. The clutch is then switched off: higher engine speed when cruising, more fuel, hotter fluid.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light or transmission warning
• No lock-up: engine speed about 100–300 rpm higher when cruising
• Higher fuel consumption, hotter transmission fluid

Common causes

• High Open or corroded harness or transmission pass-through connector
• Medium Converter clutch solenoid coil open
• Medium Internal transmission harness or mechatronic unit
• Low Driver stage in the module faulty
• Low FCA: actual converter slip (clutch wear, fluid) or software

Likelihood is a general estimate across vehicles; your make and model may differ.