P0744 Torque Converter Clutch Circuit Intermittent OBD-II Trouble Code Technical Description Article by Dan Weller ASE Certified Master Technician Torque Converter Clutch Circuit Intermittent This diagnostic trouble code (DTC) is a generic OBD-II powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may vary depending on the model. What does that mean? Modern vehicles equipped with automatic transmissions / transaxles use a torque converter between the engine and transmission to increase the engine torque output and drive the rear wheels. The engine and transmission are actually connected by a fluid coupling mechanism inside of the torque converter which is what multiplies the torque until the speeds equalize and create a "stall" speed where the difference in actual engine RPM and transmission input RPM is around 90% efficient. Torque converter clutch (TCC) solenoids commanded by the Powertrain control module/Engine control module (PCM/ECM) or the Transmission control module (TCM) to direct hydraulic fluid and engage the torque converter clutch to create a solid coupling and increase efficiency. The transmission control module has detected a fault with the circuit that operates the torque converter clutch solenoid. Note: This code is similar to codes P0740, P0741, P0742 and P0743. There may be other diagnostic trouble codes associated with the transmission control module that can only be accessed by using an advanced scan tool. If any additional transmission related DTC's appear in addition to the P0744, an electrical failure is likely. Symptoms Symptoms of a P0744 trouble code may include: Intermittent Indicator Lamp (MIL) illuminated (a.k.a. Check Engine Light) Minimal decrease in fuel economy, this will not affect engine performance Potential Causes Causes of this DTC may include: Wiring harness to transmission damaged, loose connection, or intermittent open/short circuit Torque converter clutch (TCC) solenoid Transmission control module (TCM) Diagnostic Steps for P0744 DTC Wiring harness - Check transmission wiring harness for damage or loose connections. Use a factory wiring diagram to locate the appropriate power source and all connection points between circuits. The transmission may be powered by a fuse or relay, and triggered by the TCM. Disconnect the transmission harness at the transmission connector, power source and TCM. Check for a short to ground inside the transmission internal wiring harness by locating the appropriate + and - pins for the torque converter clutch solenoid. Using a digital volt ohm meter (DVOM) set to ohms scale, check for a short to ground in the circuit with the positive lead on either pin and the negative lead to a known good ground. If resistance is low, suspect a short to ground the internal harness or the TCC solenoid - removing the transmission oil pan may be necessary to further diagnose the TCC solenoid. Test the wiring between the TCM and the wiring harness connector at the transmission case using the DVOM set to ohms. Check for a possible short to ground by moving the negative lead on the DVOM to a known good ground, resistance should be very high or over limit (OL). Test the wiring for the control circuit between the TCM and the wiring harness connector at the transmission case using the DVOM set to volts scale - it may be necessary to remove the pin from each side of the harness connector to isolate it from the harness while it is still plugged into the TCM and transmission case. With the positive lead on either end of the wiring and the negative lead to a known good ground, check for the presence of battery voltage with the key on/engine off. If voltage is present, suspect a short to power and determine the source of the short circuit in the wire harness assembly. Hint: Wiggling the wire harness and connectors while testing may help locate an intermittent short to power or ground. Torque converter clutch (TCC) solenoid - Check the resistance in the TCC solenoid and internal transmission wiring at the transmission case after removing the transmission harness plug (if applicable, some makes/models use a TCM bolted directly to the transmission case). Some makes/models use a transmission wire harness with the TCC solenoid and internal harness as a single unit. The DVOM should be set to ohms scale with the positive lead and negative lead on the pins for the TCC power and control circuit. Resistance should be within manufacturers specifications, if it is very high or over limit (OL), remove the transmission oil pan to inspect the solenoid inside the transmission if possible. Check for voltage on the power side circuit of the TCC solenoid with the key on/engine off and harnesses plugged or at the wire harness connector at the TCM with the DVOM set to volts scale, positive lead on the control side of the solenoid and the negative to a known good ground with the vehicles key on/engine off, battery voltage should be present. Tap the solenoid and wiggle the wiring to determine if a short to power or ground exists. Transmission control module (TCM) - Since the torque converter clutch is only activated during certain driving conditions, it will be necessary to monitor the TCM with an advanced scan tool to determine if the TCM is commanding the TCC solenoid and what the actual feedback reading is at the TCM. The TCC solenoid is normally controlled by a duty cycle to engage a more comfortable torque converter cluch engagement To test if the TCM is actually sending the signal, a graphing multimeter set to duty cycle or a digital storage oscilloscope will be required as well. The positive lead is probed into the wiring harness plugged into the TCM and the negative lead to a known good ground. The duty cycle shold be the same as being commanded by the TCM in the advanced scan tool reading. If the cycle is intermittent on rough road conditions, it may be a wiring fault. Re-check connections and if all wiring / solenoid is OK or if road conditions do not coincide with the intermittent readings, the TCM may be at fault.
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