Pressure Control Solenoid B Stuck On
The transmission's pressure control solenoid B is stuck in the open position, preventing proper fluid pressure regulation. Think of it like a stuck faucet that won't close—the fluid keeps flowing uncontrolled.
The ECM monitors solenoid B's electrical resistance and duty cycle commands to verify proper on/off switching. When the solenoid remains energized despite deactivation commands, the ECM detects abnormal pressure control and sets the fault. The solenoid should cycle between commanded states; continuous activation indicates a stuck-on condition.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Solenoid B Duty Cycle Response | 0-100% cycling with command changes | Remains at 100% or high state when commanded off |
| Line Pressure at Solenoid B | Regulated per gear selection (typically 40-90 psi) | Excessive/unregulated pressure due to stuck-on valve |
Code P0781 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, P0781 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.