P0740
Torque Converter Clutch Circuit/Open.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 7
- AreaTransmission
- 40
- FaultThe specific fault in that area
What it means
P0740 is the generic code for a fault in the torque converter clutch (TCC) circuit, with the SAE description being a circuit or open fault. The transmission control unit saw the TCC solenoid circuit not behaving as commanded, for example an open circuit, a wiring fault or a solenoid that does not respond. Exact monitoring and set conditions vary by manufacturer and transmission, so the details depend on the model.
Symptoms
- Malfunction indicator lamp on, possibly with a transmission warning light
- Torque converter does not lock up, so engine revs stay higher at cruising speed
- Increased fuel consumption
- Shudder or judder at steady speeds
- Transmission running hotter than normal
- Car may stall or hesitate when slowing to a stop if the clutch stays applied
Possible causes
- Faulty torque converter clutch solenoid (open or shorted winding)likely
- Damaged, chafed or corroded wiring between the solenoid and the transmission control unitlikely
- Poor connection at the transmission internal harness connector or control unit plugpossible
- Contaminated, degraded or low transmission fluid affecting the solenoid and valve bodypossible
- Sticking or worn valve body components or internal transmission wearpossible
- Faulty transmission control unit or driver circuitrare
- Outdated control unit software where a known fault is documented for that modelrare
How to diagnose
- Read all stored codes and freeze frame data, noting speed, load, gear and temperature when the code set, and check for other transmission or engine codes
- Check the transmission fluid level and condition (where a dipstick is fitted), looking for burnt smell, dark colour or debris, and follow the manufacturer's procedure for the model
- Inspect the wiring and connectors to the transmission and control unit for damage, corrosion, fluid ingress or chafing
- Check for relevant technical service bulletins or software updates for the model and transmission
- Using live data, command the TCC and watch the requested and actual lock-up status and slip speed
- Measure the solenoid resistance and compare it with the manufacturer's specification, then check the circuit for continuity, short to earth and short to supply
- Check the supply voltage and earth at the solenoid circuit with the connector disturbed to find intermittent faults
- Where the circuit and solenoid test fine, investigate the valve body and internal transmission condition as the procedure for that model directs
How to fix
- Repair or replace damaged wiring and clean or replace faulty connectors
- Replace the TCC solenoid if it is out of specification, following the procedure for that transmission
- Correct the fluid level and change the fluid and filter with the specified type if it is degraded or contaminated
- Repair or replace the valve body or worn internal components if diagnosis shows sticking or wear
- Update the control unit software only where an outdated calibration is a documented cause for that model
- Replace or repair the transmission control unit only after the wiring and solenoid are proven good
Can I keep driving?
The car can usually be driven for a short time to get it checked, but avoid heavy loads and long journeys. Continued driving without lock-up can overheat the transmission and raise fuel use, and the fault may get worse.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.