P0740: the torque converter lock-up circuit has a fault
The torque converter connects the engine to the gearbox through fluid rather than a direct mechanical link, and a lock-up clutch inside it can clamp the two together directly once the car is up to speed, to stop power being wasted. This code means the electrical circuit that controls that clutch isn't behaving the way the gearbox computer expects. It covers the wiring, connector and solenoid together, without saying which one is at fault.
You might notice
- The engine may feel like it's slipping or surging at a steady speed
- The engine warning light comes on
- torque converter
- — the part that connects the engine to the gearbox through fluid rather than a direct mechanical link
- lock-up clutch
- — a clutch inside the torque converter that clamps the engine and gearbox directly together once the car is up to speed
- gearbox computer
- — the separate computer, distinct from the engine control unit, that runs an automatic gearbox
What the code itself says
P0740 is a powertrain (engine, gearbox and drive system) code, and the 0 after the letter means it is a generic code with a standard meaning.
Grouped here as: Gearbox control — Gear selection, shift quality, fluid condition and the sensors and solenoids the gearbox's own control module reads. That grouping is ours, to help explain the code. The code's official family is the letter at the start.
This page is generic. Your car isn't.
A code on its own only tells you what the sensor saw, not what's actually wrong — and that changes next to your other codes. Read this one together with the rest of your scan and we'll work out what's really going on.
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