P0411: Secondary Air Injection System Incorrect Flow Detected
P0411 means the secondary air injection (AIR) system is moving a different amount of air than the engine computer expects after a cold start. The car usually drives normally, but it turns on the check engine light and produces higher emissions right after a cold start.
You can keep driving
Limp mode is not expected with this code and the car normally drives as usual. The only effect is higher emissions during cold starts, so have it repaired in reasonable time, especially if you need an emissions test.
What it means
After a cold start, the AIR pump blows fresh air into the exhaust right behind the exhaust valves. This burns off unburnt fuel and helps the catalytic converter (the part that cleans exhaust) warm up faster. A shut-off valve opens the air path and keeps hot exhaust from flowing back into the pump. P0411 is set when the measured air flow does not match the expected value. Some systems judge this indirectly from the oxygen sensor or the fuel correction. GM systems measure it directly with a pressure sensor between the pump and the valve and compare the reading with a model while the pump and valve are on. In the reference data, a GM system from 2018 sets the code when the pressure deviates by more than 5.0 kPa above or 4.9 kPa below the model, and the warning light comes on after two trips. The test only runs on a cold engine after a long stop, so short trips with a warm engine do not complete it.
Likely causes
- Pump weak or failed (water, filter debris)Very likely
Water or debris from the filter can wear out or block the pump, so it delivers too little air.
- Combination valve partly stuck or check valve faultyVery likely
A valve that does not open fully restricts the air, and a faulty check valve lets the flow differ from what is expected.
- Hoses blocked, leaking or off; ducts in the head carboned upPossible
Any restriction or leak in the air path changes how much air actually reaches the exhaust.
- Pressure sensor port blocked or sensor drifting (pressure-sensor systems)Less likely
A blocked port or drifting sensor gives a wrong reading even when the air flow is fine.
- Pump relay or supply with contact resistanceLess likely
Poor electrical contact can leave the pump with too little power to deliver the expected flow.
What you may notice
- Check engine light on
- Secondary air readiness not set, which matters for an emissions test
- Pump silent after a cold start, or unusually loud
- Car drives normally, but cold-start emissions are higher
What to check, cheapest first
- 1Start the engine cold after it has sat for a long time and listen for the AIR pump running briefly. Silence or an unusually loud noise points to the pump. · you can do it
- 2Look over the AIR hoses and connections for cracks, loose or disconnected ends, and signs of water or debris. · you can do it
- 3Check the pump fuse and relay, and look for corroded or loose connectors at the pump and relay. · you can do it
- 4Read the stored code and freeze-frame data with a scan tool, and check for related codes such as P0410 or P2431. · mechanic
- 5Command the pump and valve on with a scan tool and compare air flow or pressure readings with expected values. Check whether the combination valve opens and the check valve holds. · mechanic
- 6Inspect for blocked hoses, carboned-up ducts in the cylinder head and a blocked sensor port, then repair or replace the faulty part and run the cold-start test again. · mechanic
Related codes
Frequently asked questions
Can I keep driving with P0411?+
Yes, usually. The car normally drives as usual, but cold-start emissions are higher, so get it fixed in reasonable time.
Can a loose gas cap cause P0411?+
No. This code concerns the secondary air system, and the reference lists the pump, valves, hoses and related parts as causes, not the gas cap.
Will P0411 pass an emissions test?+
Probably not. The check engine light is on and the secondary air readiness is not set, which can cause a fail.
Why did the light not go out after the repair?+
The test only runs on a cold engine after a long stop, so short warm trips do not complete it. Let the car sit, then do a cold start and drive.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10