Secondary air injection helps clean up emissions during the first minute or two after a cold start. By pumping fresh air into the exhaust stream, it feeds extra oxygen that burns off leftover fuel and rapidly heats the catalytic converter so it starts cleaning sooner.
Animated: how a Secondary Air Injection actually works
🔧 How It Works, Step by Step
1
Cold start triggers pump
On a cold start the computer switches on the air pump.
2
Air enters exhaust
Fresh air is forced into the exhaust ports or manifold.
3
Leftover fuel burns
Extra oxygen lets unburned fuel in the exhaust combust.
4
Converter heats fast
The added heat brings the catalytic converter up to operating temperature quickly.
5
Pump shuts off
Once the engine and converter warm up, the system shuts down.
🧩 The Key Parts
Air pump
Blows fresh air into the exhaust during cold starts.
Control valve
Directs air into the exhaust only when needed.
Check valve
Stops hot exhaust from flowing back into the pump.
Plumbing and hoses
Route the air from the pump to the exhaust ports.
📋 Free OBD2 Code Cheat Sheet
The 50 most common check engine codes with likely cause and DIY fix cost. Sent once.
🩺 Signs of a Failing Secondary Air Injection
Check engine light with air injection codes
Loud whirring or grinding at cold start
Failed emissions test
Rough running only right after startup
Pump running longer than normal
Moisture-related pump failure
⚠️ Common Problems
Pump failure
Moisture and rust seize the air pump, so it fails to deliver air and sets a code.
Stuck valve
A control or check valve sticks, letting exhaust damage the pump or blocking airflow.
Clogged passages
Carbon builds up in the injection ports, restricting airflow into the exhaust.
💰 Cost to Fix
$300-$1000typical range to repair or replace, parts and labor
❓ FAQ
What does a P0410 code mean?
It indicates a fault in the secondary air injection system, often a failed pump, stuck valve, or blocked passage.
Why does my car whir loudly for a minute after cold start?
That is the secondary air pump running to help the converter warm up. It should stop once the engine warms.
Can I ignore a secondary air injection fault?
The car still runs, but it will fail emissions and produce more pollution on cold starts, so repair is recommended.