Error Code P0411 is described as Secondary Air Injection Incorrect Flow Detected.


Secondary Air Injection is actually an emission control that uses a pump to send fresh outside air to the Exhaust System (to the exhaust manifolds or exhaust ports) during cold engine start up, or when the engine is in open loop and pre-catalytic converter during in closed loop. It is either electric or turned by the drive belt. This process helps reduce the vehicle’s emission of harmful gases such as CO (Carbon Monoxide), HC (hydrocarbon), NOx (Nitrogen Oxides), and convert them into fresh air such as CO2 (Carbon Dioxide), HC (Hydrocarbons) and even H2O (water vapor).

There’s a check valve for this component located at the air supply line, keeping the exhaust gas from getting to the pump. There’s also a cutoff valve to control the airflow, which can be either electrically controlled or vacuum controlled. When the PCM (Powertrain Control Module) activates these valves, the vacuum automatically travels to the cutoff valve, opening it and allow fresh air to flow. Some Air Systems only allow fresh air to flow, while some only comes with a check valve and the flow is regulated by an air pump with electromagnetic clutch (similar to an A/C clutch).

During hard acceleration, the air pump is deactivated, preventing backfire from the exhaust. To self-check, the PCM will activate the Air System and allow fresh air to get to the exhaust system. The Oxygen sensor will then recognize the fresh air as lean condition, and activate its short term fuel trims to move positive direction to compensate and make a good air fuel ratio The PCM expects this process within a few seconds of self-test. If it is unable to see the short term fuel trim rise, the PCM will then intercept and look at this condition as a malfunction in the Air System, which will trigger the Error Code Po411.

Common Symptoms

  • Check Engine light is on
  • Engine runs rich (counterintuitive process – explanation below)
  • Backfiring in the exhaust during hard acceleration
  • Squealing belt

Possible Causes

  • Defective or missing check valve
  • Damaged or plugged Air pump intake port
  • Faulty Air pump clutch or Air pump relay
  • Damages (holes) in exhaust components
  • System restriction due or plugged with carbon
  • Defective Air control solenoids or vacuum lines

How to Check

When the Error Code P0411 is set, it means the PCM doesn’t see the front O2 sensor voltage drop enough when the Air Pump is supposed to add outside air to the exhaust system and burn off excessive CO and HC that are generated during cold start of the engine. Thus, to test, one needs a data streaming tool during a cold startup. Some scan tools provide the methods to test SAS (Secondary Air System) when the engine is already warmed up.

Cold start the vehicle and observe the front O2 sensor from the scan tool data stream. After around 5 – 10 seconds, you may hear the secondary air pump start, its sounds is similar to a vacuum cleaner running under the hood. When the pump kicks in, the O2 sensor voltage should go to less than 125mV. If you can’t get this figure, then there’s a fault in your SAS.

  • If you don’t hear the motor of the Air Pump start, then check the SAS Air Pump and relay.
  • If you can hear the motor, then check the components that controls the Air delivery, including the Air Management Valve Solenoid the Air Management Valve, rubber hoses, passages and metal piping.
  • For vehicles with V6 or V8 engines, if both front O2 sensors don’t drop to below 125mV, then blow in the Air Management Valve(s). These valves should flow evenly.

Note: For GM vehicles, you need to replace the check valves as a set or code will keep re-setting. This is because the PCM needs to see an even drop in voltage of the front O2 sensor.

How to Fix

If you have a scan tool with Key on, Engine off (KOEO), then set the Air pump on. This should activate easily. If it doesn’t, then remove and check the Air pump relay, look for signs of discoloration or melting caused by heat. Repair as necessary.

With the ignition on (engine off), check the battery voltage of switched battery feed to the relay, as well as the relay control circuit. If both are absent, check circuit for blown fuse or open/short in the wiring. Repair the cause of the short and retest. If both are present, then use a jumper to the battery feed to Air pump the feed circuit through a fused jumper. This should activate the pump. If not, then check for forward and ground present at the Air pump (jumpered). If there’s still no voltage or ground present at pump, repair open in wiring harness. If voltage ground is present, but pump is still unable to run, then you may have a bad Air pump. If after you jumper the Air pump feed circuit the pump activates, then you have a defective Air pump. Replace for a new one and retest.

If the scan tool is able to activate the Air pump with key on engine running (KOER), activate the Air pump solenoid valve on and see whether there’s vacuum to the cutoff valve. There should be a vacuum to open the valve. You can check the vacuum solenoid valve of the Air pump for vacuum supply from the manifold if there’s no vacuum present. If there is vacuum, then you may have a damaged vacuum solenoid. Replace it to fix to problem.

If there’s no vacuum present at the supply to the vacuum solenoid, then inspect for damaged or plugged vacuum line or vacuum port. However, if the cutoff valve has vacuum, then turn off the engine and use a vacuum pump to supply vacuum to the cutoff valve and see if it holds a vacuum and if air can flow through when vacuum is applied. If it is unable to hold the vacuum or the valve is unable to flow upon application of vacuum, then you need to replace your cutoff valve. If your cutoff valve works just right, then check the valve for any obstruction or see if it’s still there. Replace as necessary.

Inspect the steel line that connects to the exhaust catalyst for any damages or holes that could send false information, include the exhaust ports in your inspection.

Parting Tips

Other related secondary air injection system error codes include P0410, P0412, P0491, and P0492.