OBD-II code · Powertrain (generic)
P0491 Secondary Air Injection System Insufficient Flow (Bank 1)
AIR system flow on bank 1 is below threshold during the cold-start self-test — typically a clogged check valve, leaking hose, or weak air pump.
Is it safe to drive with P0491?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyCheck valve clogged with carbon
- PossibleAir pump weak
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.7–3 h
- Emissions test
- Likely to fail
- Parts involved
- Secondary Air Injection Pump, Secondary Air Check Valve
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.