DTC 78 - WASTEGATE Solenoid Fault: Notes

The PCM operates a solenoid to control boost. This solenoid is normally open. By providing a ground path the PCM energizes the solenoid which then allows vacuum to pass to the wastegate valve. During normal operation, the PCM compares it's wastegate duty cycle signal with the boost signal and makes corrections in the 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 will shut down. Reduce maximum fuel.

NOTE: Test numbers refer to numbers on diagnostic chart.

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