Fault-Code Library · Secondary air
P0411: Secondary-air injection incorrect flow
The ECU does not see the expected oxygen-sensor response when the secondary-air system runs on cold start.
Common symptoms
- •Engine warning light
- •Noisy air pump
- •Cold-start emissions fault
- •Usually normal drivability
Likely causes
- •Failed secondary-air pump
- •Blocked passages
- •Stuck combi valve
- •Vacuum or relay fault
First checks
- •Confirm pump operation on cold start
- •Check valve and vacuum control
- •Inspect passages for carbon blockage
Important
The pump may be only one part of the system; blocked passages are common on older engines.
A fault code identifies a detected condition, not a failed part. Confirm manufacturer-specific subcodes and live data.
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