Transmission System MIL Fault
Your transmission control system detected a problem and lit up the check engine light as a failsafe. Think of it like your car's transmission is trying to tell you something is wrong with how it's communicating or operating.
The ECM monitors transmission solenoid operation, fluid pressure sensors, and shift signal timing to ensure smooth gear transitions. When voltage, resistance, or response times fall outside expected parameters, the MIL fault is triggered as a protective measure.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Solenoid coil resistance | 5-20 ohms | Open circuit (>100 ohms) or short (<1 ohm) |
| Fluid pressure sensor voltage | 0.5-4.5V during operation | <0.2V or >4.8V indicating sensor malfunction |
Code P1780 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, P1780 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.