DTC 78, WASTEGATE Solenoid Fault - "P" Series: Notes

PCM operates a solenoid to control boost. This solenoid is normally open. By providing a ground path PCM energizes solenoid which then allows vacuum to pass to wastegate valve. During normal operation, PCM compares its wastegate duty cycle signal with boost signal and makes corrections in duty cycle accordingly.

DTC 78 will set when: 

• RPM greater than 1800.
• Fuel rate greater than 20 mm.
• Boost pressure greater than or less than desired (internal to PCM).

PCM will default to boost shutdown. Reduce maximum fuel. 

1. This step checks for a good vacuum source.
2. This step checks for a faulty vacuum line or pump.
3. This step checks the solenoid wiring.