Summary
P0740 is an electrical circuit code indicating a fault in the torque converter clutch (TCC) solenoid circuit. The TCM detected an open, short, or out-of-range signal when commanding the TCC solenoid. The TCC solenoid controls the lockup clutch inside the torque converter, which eliminates slippage at highway speed for better fuel economy. The most common cause is a failed TCC solenoid (40%), followed by wiring problems (25%) and connector corrosion (15%). This is an electrical issue — not a performance or slipping complaint.
Severity: Moderate — fuel economy loss and potential for torque converter overheating
Safe to drive: Generally safe for short trips — avoid long highway driving
Repair cost: $15–$900+ depending on cause
DIY difficulty: Moderate to Advanced
What does P0740 mean?
The torque converter clutch (TCC) is a lockup mechanism inside the torque converter. At highway speed, the TCM energizes the TCC solenoid, which opens a hydraulic circuit to engage the lockup clutch. This creates a direct mechanical connection between the engine and transmission, eliminating the inherent slippage of the fluid coupling. The result is better fuel economy and lower transmission temperatures at cruising speed.
P0740 is specifically a circuit code — the TCM tried to command the TCC solenoid and the electrical response was abnormal. This could mean an open circuit (no current flow), a short circuit (current going where it shouldn't), or the current draw didn't match what the TCM expected for a functioning solenoid. The TCM monitors current flow through the solenoid driver circuit to detect these faults.
Symptoms typically include: slightly worse fuel economy (2–5 MPG), the engine RPM staying slightly higher than normal at highway cruise (no lockup), and possibly a shudder or harsh engagement if the solenoid is intermittent. Some drivers don't notice any driveability change and only discover the code during a routine scan.