Torque Converter Clutch Control Error
The torque converter clutch (which locks the transmission fluid coupling for efficiency) isn't engaging or disengaging properly, similar to a car's manual clutch stuck between fully engaged and disengaged. The ECU detects a mismatch between expected and actual converter behavior.
The ECM monitors torque converter clutch solenoid voltage and transmission fluid temperature to determine if the clutch is locking and unlocking at appropriate times. It compares actual engine and transmission speed ratios against predicted values to detect control errors.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Solenoid Duty Cycle | 0-100% PWM response within timing window | No response or stuck at extreme values |
| Speed Ratio (Engine RPM / Trans Output RPM) | 0.85-1.05 when locked | Below 0.80 or above 1.10 persistently |
Code P1746 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1746 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.