Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC 78, WASTEGATE Solenoid Fault: 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.
- This step checks for a good vacuum source.
- This step checks for a faulty vacuum line or pump.
- This step checks the solenoid wiring.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.