What does it mean?
P1620 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Supercharger Bypass Valve Control Circuit Open .
Symptoms
- MIL (check engine lamp) on
- Loss of boost and noticeably reduced power under acceleration
- Or the opposite, boost present when it should be bypassed, with harsh response off idle
- Supercharger whine at light throttle when the bypass should be open
- Higher fuel consumption
- Unstable idle or a slight surge in some cases
Likely causes
- Open circuit in the control wire between the module and the bypass valve solenoid
- Solenoid winding open internally
- Corroded, wet or backed-out terminals at the valve connector
- Blown fuse or an open supply feed to the solenoid
- Harness routed near the supercharger and heat damaged, or chafed against a bracket
- Split vacuum hose or a perished actuator diaphragm where the valve is vacuum operated
- Module output driver failure, the least likely cause
How to fix it
- Command the bypass valve with the scan tool output test and listen or watch for movement
- Unplug the solenoid and measure its winding resistance against specification; an open winding confirms the component
- Check for supply voltage at the connector with the ignition on and test continuity of the control wire back to the module
- Inspect the connector and the harness near hot components for melted insulation and chafe damage
- Check the vacuum hose, the actuator diaphragm and the valve linkage for splits and binding
- Repair the open circuit or replace the solenoid, then repeat the output test to confirm operation
- Evaluate the module driver only once the circuit and the component have both tested good