P0740
PowertrainTorque Converter Clutch Circuit Malfunction
The torque converter clutch is the bit that locks the engine and gearbox together at cruising speeds so the engine isn't constantly spinning the converter through fluid. P0740 means the gearbox control module has spotted an electrical fault in the circuit that operates the solenoid for that lock-up clutch. When it can't lock up properly you lose that direct drive, so the engine revs higher than it should at a steady cruise, fuel economy drops, and on a lot of cars you'll feel a shudder. Whether it's a £150 solenoid or a gearbox-out job depends entirely on what's behind the code, and that's worth knowing before you spend anything.
ⓘ Information only. This page provides general educational information about fault code P0740. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0740 mean?
P0740 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Torque Converter Clutch Circuit Malfunction.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, sometimes with the gearbox in limp mode
- • Revs sitting higher than normal at a steady motorway cruise, say 70 mph in top
- • Fuel economy noticeably worse, often the first thing owners actually notice
- • A shudder or vibration as the car tries to lock up, typically around 30 to 40 mph
- • Harsh or delayed shifts, worse pulling away from a standstill
- • The engine stalling or nearly stalling as you come to a stop after a fast run, because the clutch won't release
Possible causes
Causes commonly associated with P0740, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Old, low or burnt automatic transmission fluid. This is where I'd look first on any high-mileage box, especially one that's never had a fluid change. Dirty fluid fouls the solenoid and the symptoms mimic an electrical fault
- 2. Faulty or stuck TCC solenoid. Common wear item, and the cheapest of the realistic fixes if the box otherwise behaves
- 3. Damaged or corroded wiring and connectors in the solenoid circuit. The gearbox connector and any harness running near the bellhousing takes heat and road muck, so check it before condemning anything internal
- 4. Blocked transmission filter starving the valve body of clean fluid, often goes hand in hand with neglected fluid
- 5. TCM fault or outdated software. Some boxes set P0740 over a software bug and a dealer reflash sorts it
- 6. Internal failure of the torque converter itself, the lock-up clutch material worn out. Less common than the cheap causes but it does happen
- 7. Worn internal gearbox components affecting fluid pressure to the converter
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read all the codes, not just this one. P0741 alongside P0740 points more at performance and slip than a pure wiring fault, and a wall of gearbox codes usually means a sick box rather than one solenoid
- 2. Check the fluid level and condition properly. Pull the dipstick where there is one, or check at the fill plug. You want it red and clean, not brown and smelling burnt. Dark, burnt fluid changes the whole conversation
- 3. Inspect the gearbox connector and harness for corrosion, melted insulation or a loose pin. Wiggle-test it with the scanner watching live data
- 4. Test the TCC solenoid circuit for continuity and resistance with a multimeter and compare against the spec for that box
- 5. Take it for a road test above 45 mph watching live data, and look at the difference between converter RPM and input shaft speed. If it commands lock-up and the revs don't drop, you've confirmed it's not just a lazy sensor reading
- 6. If the wiring, fluid and solenoid all check out, the converter or internals come into question, and that's the point to get the pan off or send it to a gearbox specialist
Common questions about P0740
Will my car fail its MOT with a P0740 stored? +
The code on its own isn't an MOT item, the tester isn't plugging in a scanner. What can fail you is the engine warning light being lit when they check the dashboard for the MIL. If you've fixed the cause, drive a few cycles to make sure the light clears and stays off before you book the test. A car stuck in limp mode could also fail on the basis it won't drive normally.
What am I looking at to put this right at a UK garage? +
Depends massively on the cause. A diagnostic check is usually £40 to £80 at an independent. If it's just the TCC solenoid and it's accessible, you might be £150 to £400 fitted. A full fluid and filter service to cure a fluid-related fault is often £150 to £300. If it's the torque converter or the box internals, you're into £800 to well over £1,500, and a main dealer can easily double that on a remanned unit. Get a couple of quotes from gearbox specialists before you let a main dealer near it, the independents who do nothing but autos are usually cheaper and know these boxes better.
How do I tell whether it's the solenoid, the fluid or the converter itself? +
Start with the fluid because it's free to look at. If it's dark and smells burnt, change the fluid and filter first, clear the code and see if it comes back, because dirty fluid causes a lot of these. If the fluid is clean and the symptoms are a shudder with the warning light, get the solenoid circuit tested for resistance and the connector checked for corrosion, that's the next cheapest culprit. If the wiring and solenoid test fine and the box still won't hold lock-up on a road test, the converter or internals are the likely answer, and that's the expensive end. Fixing the cheap causes first is the sensible order, just don't keep clearing the code and ignoring it.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →