Cause
Failed secondary air injection pump
The pump that blows fresh air into the exhaust ports for the first minute or two after a cold start, so unburnt fuel keeps burning in the manifold and brings the catalyst up to temperature faster. The system runs only briefly and only when cold, which is the fact that makes it hard to test: by the time the vehicle is on a ramp with a scan tool connected, the pump is no longer supposed to run.
This entry is the pump failing electrically or losing output, as opposed to one that has mechanically seized — the two are separated in this corpus because they present differently. A failing pump still turns but moves too little air, so the system stores an insufficient-flow or incorrect-flow code while the pump is plainly audible. A pump you can hear is not a pump that is working, and that is the trap.
Water is the usual killer. The pump sits low, its intake draws from a wheel arch or the engine bay, and condensation from the exhaust side can find its way back through a failed check valve into the pump housing. So a failed pump argues for inspecting the check valve in the same visit — a new pump behind a failed valve is a repair with a known expiry date.
Typically a moderate job.
Codes this can cause (5)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0410 Secondary Air Injection System A Likely for this code Moderate
- P0411 Secondary Air Injection System A Incorrect Flow Detected Likely for this code Moderate
- P0491 Secondary Air Injection System Insufficient Flow — Bank 1 Low
- P0492 Secondary Air Injection System Insufficient Flow — Bank 2 Low
- P2258 Secondary Air Injection System Control A Circuit High Moderate
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