Torque Converter Clutch Circuit/Open
The Powertrain Control Module (PCM) or Transmission Control Module (TCM) detected an open circuit or electrical malfunction in the Torque Converter Clutch (TCC) solenoid circuit. This means the computer cannot properly control the TCC to lock up the torque converter at cruising speeds.
While the vehicle is usually safe to drive in the short term, prolonged driving without TCC lock-up can cause the transmission to overheat and reduce fuel economy. It should be diagnosed soon to prevent internal transmission damage.
Common symptoms
- Illuminated Check Engine Light
- Decreased fuel economy at highway speeds
- Engine RPMs remain higher than normal at cruising speeds
- Transmission fluid overheating
- Harsh or delayed transmission shifting
Likely causes
- Defective Torque Converter Clutch (TCC) solenoid
- Damaged, corroded, or loose wiring and connectors in the TCC circuit
- Dirty or contaminated transmission fluid restricting solenoid operation
- Faulty torque converter assembly
- Internal transmission valve body issues
- Failing Transmission Control Module (TCM) or PCM
What to check before replacing parts
Check the transmission fluid level and condition
Look for: Low fluid levels or burnt, dark, and contaminated fluid which can impede solenoid operation and indicate internal wear.
Inspect the TCC solenoid wiring harness and connectors
Look for: Frayed wires, melted insulation, or corroded pins that would cause an open circuit or poor electrical connection.
Test the TCC solenoid resistance using a digital multimeter
Look for: Resistance readings outside the manufacturer's specified range, indicating an internally open or shorted solenoid.
Command the TCC solenoid on and off using a bi-directional scan tool
Look for: A lack of an audible click from the transmission or no change in transmission data, confirming the solenoid is not actuating.
Check the TCC circuit for power and ground at the transmission connector
Look for: Missing voltage or ground signals from the PCM/TCM, which points to a wiring issue between the control module and the transmission.
This page explains the generic P0740 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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