What does it mean?
Modern vehicles equipped with automatic transmissions/transaxles use a torque converter between the engine and transmission to increase engine torque and drive the rear wheels.
The engine and transmission are actually connected by a fluid coupling mechanism inside the torque converter, which multiplies torque until the speeds equalize and create a “stall speed” where the difference between the actual engine speed and the transmission input speed is about 90% efficient. The Torque Converter Clutch (TCC) solenoids controlled by the Powertrain Control Module/Engine Control Module (PCM/ECM) or the Transmission Control Module (TCM) direct the hydraulic fluid and engage the torque converter clutch to create a solid coupling and increase efficiency.
The Transmission Control Module detected a malfunction in the circuit that operates the torque converter clutch solenoid.
Note: This code is similar to codes P0740, P0741, P0742, P0743, P2769, and P2770.
There may be other diagnostic trouble codes associated with the Transmission Control Module that are only accessible using an advanced scan tool. If additional transmission-related DTCs appear in addition to P0744, an electrical failure is likely.
Symptoms
Symptoms of a P0744 trouble code may include:
Intermittent Malfunction Indicator Light (MIL) is on (e.g., check engine light)
Minimal decrease in fuel economy, this will not affect engine performance
Potential Causes
Causes
of this DTC may include:
Damaged transmission wiring harness, loose connection, or intermittent open/short circuit
Torque Converter Clutch (TCC) solenoid
Transmission Control Module (TCM)
Diagnostic Steps
for P0744 DTC
Wiring Harness – Check that the transmission wiring harness is not damaged or loose. Use a factory wiring diagram to locate the appropriate power source and all connection points between the 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 internal transmission wiring harness by locating the appropriate + and – pins for the torque converter clutch solenoid.
Using a digital volt ohm meter (DVOM) set to an ohms scale, check for a short to ground in the circuit with the positive lead on one of the pins and the negative lead on a known good ground. If resistance is low, suspect a short to ground in the internal harness or TCC solenoid – removal of the transmission oil pan may be necessary to further diagnose the TCC solenoid.
Test the wiring between the TCM and the transmission case wiring harness connector using the DVOM set to ohms. Look for a possible short to ground by moving the DVOM’s negative lead to a known good ground; the resistance should be very high or above the limit (OL).
Test the control circuit wiring between the TCM and the wiring harness connector in the transmission case using the DVOM set to the 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 connected to the TCM and transmission case. With the positive lead at each end of the wiring and the negative lead on a known good ground, check for battery voltage with the key on/engine off. If voltage is present, suspect a short to power and determine the source of the short in the wiring harness.
Tip: Jiggling the wiring harness and connectors during testing can help locate an intermittent short to power or ground.
Torque Converter Clutch (TCC) Solenoid – Check the resistance of the TCC solenoid and internal transmission wiring to 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 wiring harness with the TCC solenoid and internal harness as a single unit. The DVOM should be set to an ohms scale with the positive and negative leads on the TCC power and control circuit pins. The resistance should be within the manufacturer’s specifications; if it is very high or above the limit (OL), remove the transmission oil pan to inspect the solenoid inside the transmission if possible.
Check for voltage on the power side of the TCC solenoid circuit with the key on/engine off and the harnesses connected or on the wiring harness connector at the TCM with the DVOM set to the volts scale, the positive lead on the control side of the solenoid and the negative on a known good ground with the vehicle key on/engine off; battery voltage should be present. Press on the solenoid and jiggle the wiring to determine if there is a short to power or ground.
Transmission Control Module (TCM) – Since the torque converter clutch is only activated under 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 to the TCM is. The TCC solenoid is normally controlled by a duty cycle to achieve a smoother torque converter lockup engagement.
To test if the TCM is actually sending the signal, a graphing multimeter set to duty cycle or a digital storage oscilloscope will also be needed. The positive lead is probed into the wiring harness connected to the TCM and the negative lead to a known good ground. The duty cycle should match what is commanded by the TCM in the advanced scan tool reading. If the cycle is intermittent under hard road conditions, it may be a wiring issue. Check the connections again, and if all wiring/solenoid is in good condition or if road conditions do not coincide with intermittent readings, the TCM may be at fault.