What does an air injection pump do?
An air injection pump, also known as a secondary air pump, injects fresh air into the exhaust stream to help oxidize unburned fuel and accelerate the catalytic converter’s warm-up, reducing emissions during cold starts.
Overview: role in the vehicle’s emissions system
Many gasoline-powered vehicles use a secondary air injection (SAI) system to curb pollutants when the engine and exhaust are not yet at their optimal temperatures. The goal is to promote rapid oxidation of hydrocarbons (HC) and carbon monoxide (CO) and to help the catalytic converter reach its light-off temperature more quickly, thereby lowering emissions during startup.
How an air injection pump works
The pump is typically belt-driven and mounted on the engine. When commanded by the engine control unit (ECU), it pushes fresh air through a network of hoses toward the exhaust manifold or catalytic converter. The system usually includes check valves or a diverter valve to prevent backflow and to control air delivery. Oxygen sensors monitor exhaust conditions and help determine when the extra air is no longer needed, at which point the system is shut off.
Timing and control
Activation is timed to coincide with cold starts and certain engine operating conditions. The ECU uses engine temperature, RPM, and other parameters to decide when to open the air valves and run the pump, typically until the catalytic converter reaches its operating temperature.
Key components and layout
Below are the core parts you’ll typically find in an air injection/secondary air system and how they connect.
- Belt-driven air pump mounted on the engine block or timing cover
- Air delivery lines that route air to the exhaust manifold or near the catalytic converter
- Check valves and/or a diverter valve to regulate flow and prevent backflow
- Motor, relay, and wiring controlled by the engine control module (ECU)
The exact arrangement varies by vehicle, but the common thread is delivering a controlled burst of air to promote oxidation in the exhaust and to heat the catalytic converter more quickly.
Common symptoms of a failing air injection pump
When the pump or its associated components fail, several telltale signs can appear. The list below highlights typical indicators.
- Illuminated Check Engine Light with secondary air system codes (e.g., P0410 or related codes)
- Reduced or absent air flow during startup or strange exhaust odors
- Unusual belt noise, squeaking, or a whine from the front of the engine bay
- Visible leaks or cracked hoses in the air delivery network
- ECU-detected anomalies in emissions-related performance during cold starts
Notes: Codes and symptoms can vary by make and model, and some modern vehicles have phased out SAI systems in favor of more advanced catalysts and exhaust aftertreatment. A professional diagnosis helps determine if the issue lies with the pump, valves, lines, or control electronics.
Diagnosing and servicing the system
If a vehicle shows signs of an air injection problem, technicians typically follow a structured diagnostic sequence to confirm the fault and determine the right fix.
- Use an OBD-II scanner to read codes related to the secondary air system (e.g., P0410, P0411)
- Inspect the belt for wear, tension, and alignment; replace if necessary
- Check electrical connections, fuses, and the pump relay for corrosion or damage
- Listen for pump operation during cold startup and verify air flow through the lines
- Inspect air lines for leaks, cracks, or blockages; test the diverter/check valves
- Consider a smoke test to identify leaks in the air delivery path
Conclusion: Diagnosing an air injection issue can require specialized tools and knowledge. In many cases, repair or replacement of the pump, valves, or hoses is necessary to restore proper emissions performance.
What to do if you’re dealing with a faulty pump
If you suspect a problem, start with a professional inspection. Depending on the findings, options may include cleaning or replacing the pump, repairing cracked hoses, or addressing faulty valves. Timely maintenance helps ensure the vehicle meets emissions standards and avoids long-term engine or exhaust damage.
Summary
In short, an air injection pump is a component of the secondary air system that adds fresh air to the exhaust to promote oxidation of pollutants and to speed the catalytic converter’s warm-up. This helps reduce emissions during cold starts. The system comprises a belt-driven pump, air lines, valves, and ECU control. When it fails, signs often include a CEL with secondary air codes, unusual belt noise, and leaks in the air-delivery network. Diagnosis and repair should be performed by a qualified technician to restore proper emissions performance and comply with regulations.
