What P0740 means
At cruise, a clutch inside the torque converter locks engine to transmission directly, eliminating the converter's fluid slip for economy. P0740 means the circuit controlling that lockup clutch is faulty — the computer commands lockup and the electrical side doesn't cooperate.
What you’ll notice
- RPM slightly high and 'soft' at highway cruise
- Fuel economy down noticeably
- Sometimes shudder as lockup tries and fails
- Running warmer on long drives
Likely causes and repair cost
Broad US independent-shop bands, parts and labour.
Can you drive with P0740?
Yes, with a heat note: an unlocked converter sheds its slip as fluid heat, so long highway pulls and towing run the transmission hotter than designed. Around town it's mostly a fuel-economy tax.
The misdiagnosis to avoid
Living with it because around-town driving feels fine. The unlock tax compounds: a few hundred RPM of permanent highway slip is heat, and heat is the primary killer of transmission fluid and clutches. The solenoid-level fix now is cheap insurance against fluid cooked into the expensive kind of failure.
How P0740 actually gets set
The transmission controller commands a shift and then checks whether the input and output speed sensors show the ratio it expected. When the measured ratio does not match the commanded gear, or a solenoid circuit does not respond, a code sets. Many of these codes therefore describe a symptom the controller observed rather than a part that failed.
What a scan tool shows that the code does not
Transmission fluid temperature, commanded versus actual gear, and solenoid duty cycles. Fluid temperature in particular explains the single most common complaint pattern in this family — faults that only appear once everything is hot, because heat thins the fluid and erodes the hydraulic pressure margin the system was relying on.
The trap with this family of codes
Accepting a rebuild quote without first checking the fluid. Low, burned or simply ancient fluid produces slipping, flaring and hard shifts, and it is two orders of magnitude cheaper than the repair it gets mistaken for. This is also the code family where a second opinion from a transmission specialist most reliably pays for itself.
What happens when you clear it
Many transmission controllers store adaptive shift learning separately from fault codes. Clearing codes without resetting adaptives, or vice versa, produces confusing results after a repair, so ask which was done.
Higher than most people assume. Every slip drags friction material off the clutch packs, and that debris circulates and accelerates wear everywhere else. A transmission fault caught early is frequently a fluid service and a solenoid; the same fault ignored for six months is a rebuild.
Describe what it’s doing in your own words and the symptom checker gives you a safe-to-drive verdict, ranked causes with costs, and notes to take to the shop — free, no sign-up.
A basic code reader costs around $25 and usually pays for itself the first time a warning light comes on. We compare them in choosing an OBD2 scanner.
Questions people ask
How much fuel is the dead lockup costing me?
Typically several percent at highway speeds — lockup exists because converters waste meaningful energy as heat at cruise. Drivers who fix a long-standing P0740 often report highway economy quietly returning to numbers they'd forgotten the car could do.
What's the difference from P0741?
P0740 is electrical — the circuit misbehaves. P0741 is performance — the circuit works, lockup is commanded, and slip is still measured across the converter: the clutch itself can't hold. Same subsystem, but P0741 points harder at the converter as hardware, and its repair conversation is bigger.