P0491 on 2011-2016 Audi Q7 — Secondary Air Injection System Insufficient Flow (Bank 1)
1 vehicles · 1 makes
Most Reported On
P0491 is an OBD-II diagnostic trouble code meaning “Secondary Air Injection System Insufficient Flow (Bank 1).” This code means the PCM determined that the secondary air injection system is delivering insufficient airflow into the exhaust on Bank 1. This system pushes fresh air into the exhaust during cold starts to help the catalytic converter warm up quickly and lower emissions. Insufficient flow means the system isn't doing its job, usually due to a blockage, leak, or weak air pump. It typically triggers the check engine light and affects cold-start emissions rather than everyday driveability. This code is most commonly reported on 2011-2016 Audi Q7.
Common Causes
Diagnostic Tools
To diagnose P0491, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
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A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
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Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
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LAUNCH CRP123X OBD-II Scanner
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Autel MaxiCOM MK808S Diagnostic Tool
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Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
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FAQ
What does P0491 mean?
P0491 stands for "Secondary Air Injection System Insufficient Flow (Bank 1)." This code means the PCM determined that the secondary air injection system is delivering insufficient airflow into the exhaust on Bank 1. This system pushes fresh air into the exhaust during cold starts to help the catalytic converter warm up quickly and lower emissions. Insufficient flow means the system isn't doing its job, usually due to a blockage, leak, or weak air pump. It typically triggers the check engine light and affects cold-start emissions rather than everyday driveability.
What are the most common causes of P0491?
The most common causes of P0491 are: Clogged or restricted secondary air injection passages, Failing secondary air injection pump, Stuck or leaking air switching/check valve, Vacuum or hose leak in the air injection plumbing, Carbon buildup blocking air delivery ports, Electrical fault in the pump or valve circuit. The specific cause varies by vehicle.
How much does it cost to fix P0491?
Repair costs vary widely depending on the root cause and vehicle.
Which vehicles are affected by P0491?
Au7o has documented P0491 across 1 vehicle models from 1 manufacturers: Audi.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.