How bad is it to drive without the torque converter locking up?

You can drive short distances safely. On the highway, you lose fuel economy and the transmission runs hotter. Avoid sustained highway trips until repaired.

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.

Codes › P0740

P0740: The torque converter lockup clutch has a circuit fault

Torque Converter Clutch Circuit Malfunction

High severityCan you keep driving?

Drive to a shop soon. The car will move, but fuel economy will drop noticeably and the transmission will run hotter without lockup. Sustained highway driving without lockup can overheat the transmission.

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 it costs

Transmission fluid and filter service$100 to $250
TCC solenoid replacement$150 to $400
Torque converter replacement$500 to $1,200 plus labor
Full transmission rebuild$1,500 to $4,000

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 the commanded TCC solenoid state and whether the converter is actually locking up based on the relationship between engine RPM and vehicle speed. Download Lewis.

Related codes

FAQ

How bad is it to drive without the torque converter locking up?: You can drive short distances safely. On the highway, you lose fuel economy and the transmission runs hotter. Avoid sustained highway trips until repaired.
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.