P0816low severityPowertrain
Downshift Switch Circuit
on 2009 Audi A8 4.2L V8 · AWD
What this code means
The PCM detected a fault in the downshift switch circuit used for manual gear selection. This affects the driver's ability to command downshifts in manual or semi-automatic modes.
Symptoms
- Manual downshift not responding
- Transmission stuck in gear
- Warning light on
Common causes
- Faulty downshift switch
- Damaged wiring or connector
- Corroded switch contacts
- Faulty PCM/TCM
Diagnostic steps
- Scan for related codes
- Test downshift switch operation
- Inspect wiring and connectors
- Verify PCM input signal
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