What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II. Although generic, specific repair steps may vary by make/model.
Secondary air injection is an emissions control that uses an air pump (electric or driven by the drive belt) to move fresh air into the exhaust manifold(s) or exhaust ports when the engine is in open loop and the pre-catalytic converter when in closed loop. This reduces hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) emissions. This fresh air helps convert carbon monoxide (CO) into carbon dioxide (CO2) and hydrocarbons (HC) into water vapor (H2O).
A check valve is located in the air supply line to prevent exhaust gases from entering the pump. A shutoff valve that controls airflow may be vacuum-operated or electrically controlled. When the powertrain control module (PCM) activates the valve, vacuum is sent to the shutoff valve to open it and allow fresh air to flow. Some systems may only have a check valve, and airflow may be regulated by an electromagnetic clutch on the air pump (similar to an A/C clutch).
During heavy acceleration, the air pump will be deactivated to prevent backfiring in the exhaust. For self-monitoring, the AIR system will be activated by the PCM, and fresh air will be routed to the exhaust system. The oxygen sensors would sense this fresh air as a lean condition, and short-term fuel trims would begin moving in the positive direction to compensate. The PCM expects this to happen within seconds during the self-test. If it does not see short-term fuel trims increase, the PCM interprets this as an AIR system malfunction, and a code will be recorded.
Other secondary air injection system fault codes include P0410, P0412, P0413, P0414, P0415, P0416, P0417, P0418, P0419, P041F, P044F, P0491, and P0492.
Symptoms
Symptoms of a DTC P0411 may include:
MIL (Malfunction Indicator Lamp) illumination
Backfiring in the exhaust under heavy acceleration
Engine running rich (counterintuitive; see explanation below)
Squealing belt
Causes
Potential causes of a P0411 code include:
Damaged or missing check valve
Clogged/damaged air pump intake orifice
Air pump clutch malfunction
Holes or damage to exhaust components
Possible Solutions
If you have access to a scan tool, with KOEO (Key On Engine Off), command the AIR pump. It should activate. If not, remove and inspect the AIR pump relay for any discoloration/melting due to heat. Repair as needed.
Key on (engine off), check battery voltage at the battery switched power supply to the relay and the relay control circuit. If neither is present, inspect the circuit for a blown fuse or open/short in the wiring. Repair the cause of the short and retest. If both are present, connect battery power to the AIR pump power supply circuit using a fused jumper. The pump should activate. If not, check for power and ground present at the AIR pump when plugged in. If there is no voltage/ground at the pump, open the wiring harness. If voltage and ground are present, but the pump still does not operate, suspect a faulty AIR pump. If after jumping the AIR pump power supply circuit the pump activates, then the issue is likely the AIR pump relay. Replace and retest.
If the scan tool activates the AIR pump, with KOER (Key On Engine Running), activate the AIR pump solenoid valve and see if there is vacuum at the shutoff valve. There must be vacuum to open the valve. If there is no vacuum, check the AIR pump vacuum solenoid for manifold vacuum supply. If vacuum is present, the vacuum solenoid is likely faulty. Replace. If no vacuum is present at the vacuum solenoid supply, look for a clogged or damaged vacuum line or vacuum orifice. But if there is vacuum at the shutoff valve, stop the engine and using a vacuum pump, apply vacuum to the shutoff valve and see if it holds vacuum and if air flows through it when vacuum is applied. If it does not hold vacuum or the valve does not flow when vacuum is applied, replace the shutoff valve. If the shutoff valve operates correctly, inspect the check valve to see if it is clogged or missing. Replace as needed.
Check the exhaust catalyst steel line as well as the exhaust orifices for damage or holes that could cause false readings.