P0411 — Secondary Air Injection System Incorrect Flow

P0411 means the secondary air injection system isn't pushing the expected amount of air into the exhaust during cold start. Carbon-clogged passages and failed air pumps are the two dominant causes.

Cost range: $150–$1,600. Severity: medium. Safe to drive? Yes. It's an emissions system fault — no immediate driveability risk, but you will fail a smog test.

Most common causes of P0411

  1. Carbon-clogged air injection passages — Very common on higher-mileage engines; the passages into the head fill with soot. ($300–$900)
  2. Failed secondary air pump — Water intrusion kills the pump motor — listen for it running at cold start. ($300–$1,200)
  3. Stuck air injection check valve — Lets exhaust back into the pump and destroys it. ($150–$450)
  4. Failed pump relay or fuse — Cheapest thing to test first. ($20–$120)
  5. Leaking or disconnected vacuum control line — The changeover valve never opens. ($50–$200)

Symptoms drivers report with P0411