SBDS Interactive Codes
Your vehicle's secondary battery disconnect system isn't communicating properly with the engine control unit. Think of it like a safety switch that's not reporting back to the main computer when it should.
The ECU monitors the secondary battery disconnect system (SBDS) which cuts power to accessories during vehicle shutdown to prevent battery drain. The ECM checks for proper signal communication and response timing from the disconnect relay module. If handshake protocols or voltage signals fall outside expected parameters, a fault is triggered.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| SBDS Relay Response Time | 50-200 milliseconds | >300 milliseconds or no response |
| SBDS Signal Voltage | 4.5-5.5 volts | <2.0 volts or >6.0 volts |
Code P1620 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, P1620 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.