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P0411 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


DTC Code P0411: Secondary air injection system incorrect flow detected


During cold start, the secondary air injection system allows fresh air from outside the vehicle into the exhaust system, that is, the exhaust manifolds and the exhaust ports. The fresh air absorbed from the environment helps to reduce the emission of harmful gases such as Carbon Monoxide (CO), Hydrocarbon, Nitrogen Oxides, and other harmful gases, by converting them into harmless gases, such as Carbon-di-Oxide (CO2), Hydrocarbons, and water vapor (H2O) which are safe for the environment.

The secondary air injection system contains important components such as the check valve which is located at the air supply line and the cutoff valve which can be electrically controlled or vacuum controlled. The function of the check valve is to prevent the exhaust gas from gaining entry back into the system through the pump, while the cutoff valve functions as a control valve for the airflow in the system.

During the intake of air into the secondary air system (SAS), the Powertrain Control Module (PCM) triggers these valves, thereby making the vacuum travel automatically to and open the cutoff valve. This is to allow fresh air to gain entry into the system, while the airflow is regulated by an air pump using an electromagnetic clutch.

Meanwhile, backfire from the exhaust is prevented during hard acceleration by the deactivation of the air pump. This then prompts the PCM to activate the air system in order to ensure that the exhaust system gets access to a sufficient amount of fresh air from the environment.

This process will further prompt the Oxygen sensor to identify the fresh air as a lean condition. Thus, activating its short-term fuel trims which serves to move it in a positive direction, compensate, and generate an appropriate air-fuel ratio. More so, the PCM expects the system to complete this self-test process within a few seconds. 

The Powertrain Control Module illuminates the check engine light and records DTC code P0411 when the system encounters difficulty in detecting the short-term fuel trim rise.


The P0411 may be caused by an array of malfunctions in the vehicle’s emission control system, the most popular causes implicated with this include;

  • Failure of the air injection pump
  • Defective air pump relay or air pump clutch
  • Defective air control solenoids or airlines
  • Excessive carbon build-up in the air injection system
  • Spoilt or perforated exhaust components
  • Damaged check valve
  • Defective wiring harness of the injection system


There are a number of symptoms that have been implicated with the diagnostic trouble code (DTC) P0411, these symptoms may affect the drivability of the vehicle in some cases and may not in some other cases. 

Nevertheless, there are some other cases where the only symptom recorded is the illumination of the check engine light and nothing more. Regardless of the effects on the drivability, some of these common symptoms of P0411 include;

  • Illumination of the check engine light
  • High fuel consumption
  • Backfiring on hard acceleration
  • Poor acceleration and rough running
  • Squealing belt (in vehicles turned by a drive belt).


Diagnosing DTC code P0411 as well as other OBD-II error codes could be tricky especially for novices, which is why we strongly recommend that the diagnosis be carried out by a professional and certified auto mechanic. However, if you are a DIY type, this simple step-by-step diagnostic process should simplify the work for you:

  • Start the diagnosis by downloading the data stream of the secondary air system (SAS) using OBD-II scan tools;
  • Cold start the vehicle and observe the front Oxygen (O2) sensor from the scan tool data stream;
  • Then, command the air pump on by putting the vehicle on Key on Engine off (KOEO);
  • After about 5-10 seconds, the Secondary Air Pump should come alive, giving off a sound similar to that of a vacuum cleaner;
  • When this happens, the O2 sensor voltage is expected to go below 125mV. Any deflection from this figure probably indicates a fault in the system;
  • When this is the case, proceed to check the components that control the air delivery, including the Air Management Valve Solenoid, the Air Management Valve, rubber hoses, passages, and metal piping;
  • On the other hand, if you notice that the secondary air pump did not start, then you should check the SAS Air Pump and Relay;
  • In vehicles with either V6 or V8 engines, if the front O2 sensor is above 125mV, we recommend you blow the Air Management Valve(s) and ensure the valves flow evenly;
  • Having completed the steps above, clear the error and check if it returns;
  • If the error persists after the steps above, visually inspect the air injection system for possible damage in the connected hoses;
  • Fix any damages that you notice in the connection;
  • Also, check for excessive accumulation of carbon in the system and clear the system of excessive carbon;
  • Lastly, inspect the secondary air injection system for any broken components;
  • Fix any broken components or replace them if fixing will not solve the problem.

Common Mistakes

When diagnosing the DTC code P0411 as well as other OBD-II codes, it is important to observe all components before deciding to either replace or fix any defective part(s) or component(s), as in most cases, defective components may be fixed by simple repair without a need for replacement.

Another common diagnostic mistake in dealing with P0411 is failure to follow the diagnostic process in the correct order or deliberate skipping of some diagnostic process. This will eventually lead to a false diagnosis and wastage of time and resources.

How Serious is P0411?

DTC P0411 is tied directly with the emission control system and as such, the only noticeable symptom observed in most cases is the illumination of the check engine light. However, the presence of P0411 will cause the OBD-II emissions to fail in many situations until the error has been resolved.


Apart from diagnosing DTC code P0411, there are some repairs that can be carried out on a vehicle with the P0411 trouble code. To repair a vehicle having the P0411 trouble code, do the following:

  • Replace the air pump
  • If the error is caused by the accumulation of carbon in the system, clear the system of the excessive carbon accumulated in it
  • Replace the air solenoids
  • Repair or replace the wiring harness of the system.


In conclusion, diagnosing P0411 is quite easy in theory but it could however be technical in practice. Therefore, if you ever encounter difficulty in diagnosing this trouble code, it is best to call the attention of an expert to look into it.

P0411 Code – What Does It Mean & How To Fix It