Emission controls · Powertrain · generic (SAE-defined)
P0411: Secondary Air Injection System Incorrect Flow Detected
P0411 means the secondary air injection system is not delivering the airflow the engine computer expects during its cold-start test.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0411 sets
When the secondary air system is commanded on after a cold start, the powertrain control module (PCM) expects the upstream oxygen sensors to read lean, or a pressure sensor to show flow. If the response is too weak, too slow, or air is flowing when the system should be off, the PCM sets P0411. The monitoring strategy and thresholds are manufacturer-specific.
Common causes of P0411
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Weak or seized secondary air pump
- Check valve stuck closed or open
- Carbon-clogged air injection ports
- Leaking or disconnected air hoses
- Faulty air pump relay
- Slow or faulty upstream oxygen sensor misreporting the test
P0411 symptoms
- Check engine light on
- Unusual pump noise at cold start, or no noise
- Typically no effect on how the vehicle drives
How P0411 is diagnosed
- Review freeze frame and check for oxygen sensor codes that could affect the test
- Confirm the pump runs at cold start and listen for unusual noise
- Inspect hoses and check valve; look for moisture or exhaust soot in the pump side
- Verify relay and power supply to the pump
- Use the scan tool to activate the system and watch for a clear lean swing on upstream oxygen sensors
- Inspect injection passages for carbon restriction
Typical fixes for P0411
- Replace a weak or seized air pump
- Replace the check or combination valve
- Clean blocked passages
- Repair hoses or replace the relay
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Commonly reported on early 2000s Toyota and Lexus trucks and SUVs, and on several European makes. Definitions can vary by manufacturer; check factory service information.
Related codes & warning lights
P0411 FAQ
What does code P0411 mean?
P0411 means the secondary air injection system is not delivering the airflow the engine computer expects during its cold-start test. The standard definition is "Secondary Air Injection System Incorrect Flow Detected."
Can I drive with a P0411 code?
Yes, usually without any drivability change. The system is used only after cold starts, but expect an emissions inspection failure until the flow problem is fixed.
Can a bad oxygen sensor cause P0411?
It can. The computer relies on the upstream oxygen sensors to verify air injection, so a lazy sensor may make a healthy system appear to have low flow.
Does P0411 damage the catalytic converter?
Not directly. The converter simply takes a little longer to warm up after cold starts, increasing emissions during that time.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.