Code P0740: Torque Converter Clutch Circuit Malfunction
If you drive a car or truck that has an automatic transmission or transaxle, a torque converter clutch is situated between the engine and transmission. This component relies on a fluid coupling mechanism to increase the torque output of the engine and power the rear wheels. Torque converter clutch solenoids may be commanded by the powertrain/engine control module or the transmission control module, depending on the vehicle. The On-Board Diagnostic trouble code P0740 is set when a control module detects a fault or malfunction involving the circuit that operates the torque converter clutch solenoid.
How Do I Detect an OBD-II Scanner Error Code P0740 Problem?
A check engine light and reduced fuel economy are often the only indications of a malfunctioning torque converter clutch circuit. Inspect the condition of the transmission wiring harness and use a digital volt/ohmmeter to check continuity and resistance in the torque converter clutch solenoid. It may be necessary to monitor the transmission control unit with advanced scan tools such as a graphing multimeter or oscilloscope. This issue is unlikely to affect engine performance, but it is still important to clear the code to achieve optimal operation.
Torque converter clutch solenoids are commanded by the relevant control module to move the fluid and engage the clutch, creating a solid coupling. If this cannot occur, the ECM, PCM or TCM will set error code P0740. This code may be set with similar codes in the range of P0741 to P0744, P2769 or P2770.
Codes P0741 and P0742 indicate that the torque converter is stuck on or off, possibly due to shorting or TCM problems, while intermittent operation sets code P0744. Heat can cause the converter to lock up, triggering code P0743. A low condition in the torque converter clutch electrical circuit is signaled by code P2769, while P2770 identifies a high condition. Experts generally suggest that more than one transmission trouble code indicates electrical failure.
What Causes a Torque Converter Clutch Circuit to Malfunction?
A hydraulic fluid coupling mechanism inside the torque converter connects the engine to the transmission and multiplies torque until speeds equalize. This establishes a “stall” speed where the difference in actual engine revolutions per minute and transmission input revolutions per minute are around 90% efficient.
The most common torque converter clutch circuit issues are related to loose connections or damaged parts, problems with the torque converter clutch solenoid or the transmission control module itself. Check connections before using a digital volt/ohmmeter to test continuity and resistance or an advanced scan tool to monitor the transmission control module.
How Do I Fix Trouble Code P0740?
Check connections between the wiring harness and the power source as well as between circuits. Disconnect the transmission harness at the connector, power source and TCM to check for continuity inside the internal wiring harness at the positive and negative leads on the torque converter clutch solenoid pins.
High or over limit resistance point toward problems in the internal harness or torque converter clutch solenoid. Set the digital volt/ohmmeter to ohms to test wiring between the TCM and harness connector at the transmission case. Check for a short to ground by moving the negative lead to known good ground.
If resistance is high or over limit, the internal harness or TCC solenoid could be the culprit. Connect the positive lead to the TCM wiring harness and the negative lead to ground to determine whether the duty cycle corresponds to TCM commands. If the problem does not involve the harness or torque converter clutch solenoid, the TCM could be the cause. These are the most common answers to the question “what does the code P0740 mean?”