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Secondary Air System Monitor

Non-Continuous

Completes within the first 2-3 minutes of a cold start. A cold soak of at least 6 hours is needed to meet entry conditions.

What This Monitor Checks

The Secondary Air Injection (AIR) Monitor verifies that the secondary air injection system is delivering the correct volume of ambient air into the exhaust manifold during cold start to accelerate catalyst light-off. The PCM commands the air pump on and checks for the expected lean shift in the upstream O2 sensor signal and corresponding fuel trim correction. Some systems also monitor the air pump relay current draw and air switching valve position to confirm mechanical operation.

Why It Matters for Emissions

Secondary air injection reduces cold-start HC and CO emissions by 50-70% by injecting fresh air into the exhaust stream, promoting oxidation of unburned fuel in the exhaust manifold and rapidly heating the catalyst to light-off temperature. Without secondary air, cold-start emissions can exceed standards for 2-3 minutes.

Drive Cycle Steps

1

Begin with a cold engine — the vehicle must have soaked until coolant temperature is below 100°F (38°C), ideally near ambient.

2

Start the engine and remain at idle — the secondary air pump will activate automatically during the first 60-120 seconds of cold start operation.

3

Do not rev the engine or drive away immediately; the PCM needs a stable idle to measure the O2 sensor lean shift caused by the air injection.

4

After 2-3 minutes of idle, drive normally for 5 minutes to complete any follow-up checks and confirm the system deactivated properly.

Prerequisites

  • Engine coolant temperature must be below 100°F (38°C) at startup — a genuine cold start is required.
  • Ambient temperature should be above 20°F (-7°C) for the monitor enabling criteria to be met.
  • No active DTCs related to the air pump relay, air switching (diverter) valves, or upstream O2 sensors.
  • Battery must be fully charged (above 12.0 volts at rest) as the air pump draws 15-25 amps during operation.

Common Failure Reasons

  • Seized or worn-out secondary air pump motor — often fails from moisture ingestion through the air filter inlet.
  • Check valve failure allowing exhaust gases to backflow into the air pump, damaging internal components and corroding the pump housing.
  • Cracked or disconnected air injection hoses/tubes, especially the rubber-to-metal transition points that deteriorate from heat cycling.
  • Failed air pump relay or corroded relay socket contacts preventing the pump from activating.
  • Clogged air injection passages in the exhaust manifold from carbon buildup, preventing airflow even when the pump is running.

Pro Tips

  • Listen for the air pump running during the first 90 seconds of a cold start — it makes a distinct whirring/blowing sound. No sound at all usually means a relay, fuse, or pump motor failure.
  • On many VW/Audi and Subaru vehicles, the secondary air system is a common failure item — aftermarket delete kits exist but will cause permanent monitor failure and emissions test issues.
  • Check the one-way (check) valve by blowing through it in both directions — it should flow freely toward the exhaust manifold and block in the reverse direction.
  • If the air pump runs but the O2 sensor doesn't show a lean shift, suspect clogged injection passages in the exhaust manifold or a stuck-closed switching valve.

Frequently Asked Questions

What does the Secondary Air System Monitor check?

The Secondary Air Injection (AIR) Monitor verifies that the secondary air injection system is delivering the correct volume of ambient air into the exhaust manifold during cold start to accelerate catalyst light-off. The PCM commands the air pump on and checks for the expected lean shift in the upstream O2 sensor signal and corresponding fuel trim correction. Some systems also monitor the air pump relay current draw and air switching valve position to confirm mechanical operation.

How do I get the Secondary Air System Monitor to set ready?

Follow the drive cycle: Begin with a cold engine — the vehicle must have soaked until coolant temperature is below 100°F (38°C), ideally near ambient. Start the engine and remain at idle — the secondary air pump will activate automatically during the first 60-120 seconds of cold start operation. Do not rev the engine or drive away immediately; the PCM needs a stable idle to measure the O2 sensor lean shift caused by the air injection. After 2-3 minutes of idle, drive normally for 5 minutes to complete any follow-up checks and confirm the system deactivated properly. Estimated completion: Completes within the first 2-3 minutes of a cold start. A cold soak of at least 6 hours is needed to meet entry conditions.

Why does the Secondary Air System Monitor keep failing?

Common failure reasons include: Seized or worn-out secondary air pump motor — often fails from moisture ingestion through the air filter inlet.; Check valve failure allowing exhaust gases to backflow into the air pump, damaging internal components and corroding the pump housing.; Cracked or disconnected air injection hoses/tubes, especially the rubber-to-metal transition points that deteriorate from heat cycling..

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Quick Info

Type

Non-Continuous

Completion

Completes within the first 2-3 minutes of a cold start. A cold soak of at least 6 hours is needed to meet entry conditions.

Resets on Clear

Yes