P0738 Fault Code in Volkswagen: Causes, Symptoms, and Fixes

DTC P0738 indicates that the Transmission Control Module (TCM) has detected an intermittent signal from the torque converter clutch (TCC) speed sensor circuit, or there’s an unexpected gear ratio between the input and output shafts, particularly during torque converter clutch operation. It usually relates to communication issues or signal inconsistencies from the output speed sensor or turbine speed sensor.

Common Symptoms:

1. Check Engine Light (CEL) ON
2. Delayed or harsh gear shifting
3. Torque converter not locking/unlocking properly
4. Transmission may slip or go into limp mode
5. Poor fuel economy
6. Unusual RPM behavior at cruising speeds

Common Causes:

1. Intermittent connection or corrosion at the speed sensor harness
2. Failing input (turbine) speed sensor or output speed sensor
3. Wiring harness damage (rubbing, pinched, moisture intrusion)
4. Defective TCM (Transmission Control Module)
5. Internal transmission problems (slipping clutches, worn solenoids)
6. Contaminated or low transmission fluid
7. Software issues in older models

Possible Fixes:

1. Scan live data to monitor sensor signals – look for drops or inconsistent readings
2. Check wiring and connectors for corrosion, loose pins, or breaks
3. Test and replace faulty speed sensors (input/output)
4. Inspect transmission fluid condition and level
5. Perform continuity/resistance checks on the sensor circuit wiring
6. Reprogram or update TCM software (if applicable)
7. In severe cases, inspect for internal mechanical damage in the transmission

Vehicles Commonly Affected:

This code appears frequently in Dodge, Jeep, Chrysler, and Volkswagen vehicles that use Chrysler automatic transmissions. It can also appear in other brands using similar torque converter and sensor systems.