Powertrain
generic / SAE
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.
SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number4 / 91
Possible causes
- Check valve clogged with carbon high
- Air pump weak medium
Inspection / repair
- Difficulty: medium
- DIY: possible
- Estimated cost: 100–800 €
- Estimated time: 0.7–3 h
- Component: secondary air injection pump
- Component: secondary air check valve
- MIL / check engine light
- emissions-relevant
Sources
References
sae:J2012