OBD codes / P0740
P0740
SeriousTorque Converter Clutch Circuit Malfunction
P0740 is usually drivable — the car works, it just cruises at higher RPM and runs the transmission warmer. The caution is heat on long highway trips and towing, both of which lean hard on the converter. Get it diagnosed reasonably soon, and start with the fluid and solenoid before anyone mentions a converter.
What this code means
At cruising speed the transmission applies the torque converter clutch (TCC) to lock the engine directly to the transmission, eliminating the converter's natural slippage to save fuel and reduce heat. P0740 means the TCC circuit itself has a malfunction — the computer commands lockup and the circuit doesn't respond correctly, whether from an electrical fault at the solenoid, wiring trouble, or a hydraulic/mechanical problem preventing proper apply. It sits between its siblings: P0743 flags a purely electrical fault, while P0741 flags mechanical slip. Most commonly the result is lockup that never engages — higher cruise RPM, worse fuel economy, more transmission heat — though some failures cause shudder or engagement at the wrong time. The causes range from a cheap solenoid or connector to valve-body or converter issues, which is why the cost spread is genuinely wide.
Symptoms you might notice
- Higher RPM at highway cruise (lockup never engages)
- Worse fuel economy
- Shudder at steady speed in some cases
- Transmission running hotter on long drives
- Check-engine light
What it costs to fix
Varies by vehicle — get it diagnosed.
The repair cost for this code depends too much on your exact vehicle and the underlying cause to quote a meaningful range. Confirm the cause first so you only pay for the fix you actually need.
Diagnose P0740 for my vehicle →Frequently asked
How is P0740 different from P0741 and P0743?
Same system, different complaints. P0743 is strictly electrical — the circuit itself tests bad. P0741 is performance — the circuit works but the clutch slips. P0740 is the general malfunction flag, which can be either, so diagnosis starts with an electrical test to sort it into one camp or the other.
Will P0740 hurt my fuel economy?
Noticeably, on highway driving. Lockup exists mainly to eliminate converter slippage at cruise; without it the engine turns extra RPM the whole trip. City driving changes less, since lockup engages mostly at steady speeds anyway.
Could a fluid service fix P0740?
It's a legitimate first move — old or contaminated fluid can stick the lockup valve and mimic solenoid failure, and it's the cheapest thing on the list. If the fault is a dead solenoid coil or broken wiring, though, fluid won't cure it; the electrical test settles the question.
Can I still tow with this code?
Better not to. Towing without lockup means constant converter slippage under heavy load — the perfect recipe for overheated fluid. Fix the circuit first; lockup matters most in exactly the situations where towing puts you.
Seeing P0740 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0740 for my vehicleSymptoms that trigger P0740
Drivers who get this code often notice one of these — each has its own likely-causes and cost guide:
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0740 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.