P0740: The torque converter lockup clutch has a circuit fault
Torque Converter Clutch Circuit Malfunction
The torque converter clutch is not locking up, so the transmission runs hotter. Get it checked within a few days and avoid long highway trips. If it slips, shudders or smells burnt, stop driving.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
At cruising speed, an automatic transmission's torque converter locks up mechanically to eliminate slip and improve fuel economy. The TCC solenoid controls this lockup. P0740 means there is a circuit fault in the TCC system. Without lockup, the transmission runs at higher temperatures and the engine uses more fuel. The solenoid is often the culprit, but low or degraded transmission fluid can also cause TCC hydraulic problems that are reported as electrical. Check fluid before condemning the solenoid.
Common causes
- Failed TCC solenoidThe solenoid that commands converter lockup fails electrically. Common on high-mileage units.
- Low or degraded transmission fluidInsufficient fluid pressure prevents the TCC from engaging hydraulically, which can register as a circuit fault.
- Wiring or connector fault at the TCC solenoidLocated inside the transmission; wiring can deteriorate from heat and fluid exposure.
- Worn torque converter clutchThe clutch material inside the converter wears out, preventing proper lockup. Requires converter or transmission replacement.
- TCM faultRare; the controller itself fails to command the solenoid. Rule out solenoid and wiring first.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- Transmission fluid and filter service
- TCC solenoid replacement
- Torque converter replacement
- Full transmission rebuild
Symptoms
- Fuel economy worse than normal, especially on the highway
- RPM stays higher than expected at highway speed
- Transmission running warmer than usual
- Check engine light on
- Possible shudder when the converter tries to lock
What to do next
Start with a transmission fluid service if it is overdue. Fresh fluid resolves a surprising number of TCC codes by restoring proper hydraulic pressure. If fluid is fine, have the TCC solenoid tested. Solenoids are often accessible in a transmission pan drop. Avoid extended highway driving until repaired.
Lewis shows live engine RPM and vehicle speed together, so at a steady cruise you can see whether RPM stays higher than it should when the converter ought to lock up. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- How bad is it to drive without the torque converter locking up?
- Without lockup, the transmission runs hotter and fuel economy drops, especially on the highway. Avoid long highway trips and get it checked within a few days. If it slips, shudders or smells burnt, stop driving.
- Can a fluid change really fix a TCC code?
- Yes, in some cases. Degraded fluid loses its friction modifier additives, which are needed for proper TCC hydraulic operation. A service is always the right first step.
- If the TCC solenoid is bad, does the whole transmission need to come out?
- On many vehicles, no. The TCC solenoid is in the valve body, accessible by dropping the transmission pan. Full transmission removal is not always required.
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