DTC 78

Wastegate Solenoid Fault:

CIRCUIT DESCRIPTION
The Powertrain Control Module (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 its wastegate duty cycle signal with the boost signal and makes corrections in the duty cycle accordingly.

DIAGNOSTIC TROUBLE CODE (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).

ACTION TAKEN (PCM will default to)
Boost will shut down. Reduce maximum fuel.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

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

DIAGNOSTIC AIDS
A vacuum leak or a pinched vacuum line may cause a DTC 78. Check all vacuum lines and components connected to the hoses for leaks or sharp bends.

Check vacuum source. A possible DTC 32 will store if there is a problem with the vacuum source. Also check for proper vacuum line routing.