P3659moderate severityPowertrain
GDI Fuel System Depressurization Valve Stuck
on 2019 Audi A6 3.0L Turbo V6 · AWD
What this code means
The fuel rail depressurization valve used during service or fuel system shutdown is stuck, causing either a fuel pressure leak-down or inability to relieve pressure.
Symptoms
- Extended cranking after sitting (valve stuck open)
- Service hazard if valve stuck closed
- Fuel pressure drops overnight
- Hard hot restart
- Fuel rail holds pressure excessively long during service
Common causes
- Valve internal seal wear
- Valve solenoid failure
- Debris holding valve open
- Corrosion on valve seat
- Wiring fault preventing valve operation
Diagnostic steps
- Monitor fuel rail pressure decay after shutdown
- Test valve solenoid operation
- Measure pressure hold time vs specification
- Inspect valve for debris or corrosion
- Command valve during service procedure
Repair notes
Replace depressurization valve. If pressure leak-down is the issue, also check fuel injector sealing. Always relieve fuel pressure safely before GDI service.
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