P0740moderate severityGenerally driveableP0740 Code: Torque Converter Clutch Circuit Malfunction
Written in plain English and reviewed by the eli5cars editorial team · Last reviewed June 2026
What it means in plain English
Automatic transmissions use a torque converter — a fluid coupling — to transmit power from the engine to the transmission. At cruising speed, a lock-up clutch inside the torque converter mechanically locks the engine directly to the transmission, eliminating fluid slippage to improve fuel economy and reduce heat. P0740 means the transmission control module detected a problem in the electrical circuit that commands this lock-up clutch — it's not engaging, not disengaging, or not behaving the way it's being told to. You may notice higher RPM than usual at highway speed, a shudder around 40-55 mph, or worse fuel economy.
Most likely causes — ranked
#1 Low or degraded automatic transmission fluid (ATF)
most likelyFix: The torque converter clutch operates hydraulically — it needs correct fluid level and condition to apply and release properly. Low fluid (from a leak) or old, burnt fluid (from a skipped service interval) is the single most common and cheapest-to-fix cause. Check the fluid level and condition per your owner's manual procedure (many modern cars require a specific check method, some with the engine running and at temperature). If fluid is low, top up and look for the leak source. If it's dark or smells burnt, a fluid and filter service is the first move before assuming a part has failed.
#2 Faulty torque converter clutch (TCC) solenoid
likelyFix: The TCC solenoid is an electrically controlled valve that directs fluid pressure to apply or release the lock-up clutch. A solenoid that's stuck, clogged with debris, or electrically failed will trigger P0740. Test the solenoid's resistance against factory spec with a multimeter (key off, connector unplugged). On many transmissions the solenoid is part of a solenoid pack inside the valve body, which changes the labor involved. Replace the failed solenoid or pack.
#3 Damaged or corroded wiring/connector in the TCC solenoid circuit
likelyFix: Wiring to internal transmission solenoids often runs through a connector at the transmission case exterior before continuing internally. Corrosion or damage at this external connector is a common and relatively cheap-to-fix cause. Inspect the connector for corrosion, bent pins, or a poor seal, and check for continuity through the harness with a multimeter. Repairing an external connector is far less invasive than internal transmission work.
#4 Worn torque converter or internal transmission mechanical fault
possibleFix: If fluid, the solenoid, and external wiring all check out, the torque converter itself may have a mechanically worn clutch plate or internal debris interfering with lock-up. This is the most expensive scenario and typically requires transmission removal or a shop with transmission-specific diagnostic experience to confirm. Get a second opinion from a transmission specialist before authorizing major work — this cause is less common than fluid or solenoid issues.
Check engine light on? Get a free code scan
If your check engine light is on, most auto-parts stores (AutoZone, O'Reilly, Advance) will read the code for FREE — no purchase required, just walk in. Bring the code back here and look it up at eli5cars.com/obd2 for the plain-English explanation.
Note: a scan only helps when there's an active fault code. For purely mechanical symptoms (noises, vibrations, leaks), a scan may show nothing — the suspects listed above are your starting point.
Want to read the codes yourself?
First, the free option: AutoZone, O’Reilly, and Advance Auto Parts read your codes for free — no purchase needed. That’s the cheapest way to get the code to look up here. If you’d rather have your own so you can check anytime (and clear a code after a fix), the Veepeak OBDCheck BLE is an inexpensive, reliable plug-in reader that pairs with a free phone app and works on any car sold since 1996.
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Frequently asked questions
Is it safe to drive with a P0740 code?
Generally yes, at least for a while. The transmission will still shift and move the car; you'll mainly notice a shudder at certain speeds, higher RPM on the highway, and reduced fuel economy. It's not an immediate safety issue, but ignoring it risks additional heat and wear on the transmission — get it checked within a couple of weeks.
Will P0740 clear itself?
It can temporarily go inactive if the cause is borderline-low fluid that gets topped off, or an intermittent connector issue. But a genuinely low/degraded fluid condition, failed solenoid, or worn converter won't resolve without a repair — the code will return.
Why does my car shudder around 45 mph with this code?
That speed range is right where many transmissions attempt torque converter lock-up. A shudder there is a classic symptom of a struggling or malfunctioning TCC solenoid, or fluid that's too degraded to engage the clutch smoothly. This is one of the more diagnostic-friendly symptoms tied to P0740 — mention the specific speed to your mechanic.
Should I just do a transmission fluid and filter service first?
Yes, in most cases this is the sensible, low-cost first step — especially if you're not sure when the fluid was last changed. It's the cheapest possible fix, it's needed maintenance regardless, and it resolves a meaningful share of P0740 cases without touching the solenoid or torque converter.