P0491 on Audi
Secondary Air Injection System Insufficient Flow (Bank 1)
P0491 on Audi vehicles indicates secondary air injection system insufficient flow (bank 1). Au7o has documented this code across 1 Audi model — most commonly on Q7. 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.
Common Causes of P0491
- •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
P0491 on Audi by Model
Audi Q7(1 issue)
- 2011-2016 Q7 3.0 TFSI Secondary-Air Carbon Restriction - P0491/P04922011-2016
Audi TSB 2033001/18 applies to 2011-2016 Q7 3.0 TFSI vehicles with more than 15,000 miles when the malfunction indicator lamp is on and P0491 and P0492 are stored together. Audi identifies carbon restriction in the cylinder-head secondary-air ports. This is not an intake-valve diagnosis and the bulletin does not establish universal valve damage, a walnut-blasting maintenance interval or a need for engine replacement.
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View P0491 across all makes →Frequently Asked Questions
What does P0491 mean on Audi?▼
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. On Audi specifically, this code is documented across 1 model.
What causes P0491 on Audi vehicles?▼
Common causes on Audi: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0491 on a Audi?▼
Repair costs vary widely depending on the root cause and specific Audi model.
Which Audi models have P0491 documented?▼
Au7o has documented P0491 on 1 Audi model: Q7.