Pressure Control Solenoid Stuck On
The transmission's pressure control solenoid is electrically stuck in the ON position, like a stuck relay that won't turn off. This prevents the transmission from properly regulating hydraulic pressure, affecting shift quality and performance.
The ECM monitors the pressure control solenoid's electrical resistance and duty cycle command versus actual pressure feedback. When the solenoid remains energized beyond expected parameters despite command signals to deactivate, the ECU detects the malfunction. The circuit is checked for continuity faults and deviation from normal operating resistance.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Solenoid Duty Cycle | 0-100% variable based on demand | Remains at 100% or stuck high despite low-pressure demand |
| Solenoid Coil Resistance | 5-15 ohms typical | Out-of-range or shorted (<2 ohms) condition |
Code P0748 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, P0748 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.