Understanding the system and symptoms
The same dashboard message can originate from several systems, and fault-code text is a starting point rather than a definitive component diagnosis. Vehicle generation, engine, transmission and equipment must be established first.
How a technician narrows down the cause
Capture a complete scan, operating conditions and repair history before clearing faults. Reproduce the concern safely, compare live data to expected system behavior, inspect relevant mechanical and electrical components, and test the suspected failure before recommending replacement.
Model-specific context: Audi S4; researched applications 2012–2014; platform S4 B8/B8.5 Sedan. Exact applicability should be checked against the vehicle identification number and equipment.
What owners may notice in researched cases
- MIL on with P0491/P0492 secondary-air insufficient-flow codes.
- MIL on with P0491/P0492.
Diagnostic observations from the source cases
The available technical cases describe checks such as Command secondary-air pump with scan tool; Inspect secondary-air ports; Inspect secondary-air passages and related components. These checks help distinguish competing causes before recommending replacement.
Possible causes identified in individual cases
The underlying causes documented in individual cases included Carbon-plugged secondary-air injection ports.; Carbon deposits in secondary-air ports, intake manifold and combination valves. These are examples of verified findings in those cases, not a prediction of what has failed on every Audi S4.
Repairs reported in the source cases
Repairs reported to resolve documented cases included Clean secondary-air ports per TSB; clear codes/adaptives; road test; Clean carbon deposits, clear codes and run monitors. A repair that succeeded on one vehicle should only be recommended for another after confirming the same fault.
Fault codes recorded in the research
Codes mentioned in the research: 16875, 16876, P0491, P0492. Codes can have different interpretations depending on model and conditions.
Verification and next steps
After correction, repeat the conditions that triggered the fault and document the verification results.
If your Audi S4 is showing these symptoms, Mich’s Foreign Cars in Hickory, NC can discuss an appropriate diagnostic appointment. Call 828-324-6012 and provide the year, engine, warning messages and any available fault codes.