P0411 Code Definition: Secondary Air Injection System Incorrect Flow Detected
Trouble code P0411 is a generic OBD-II DTC (digital trouble code) which indicates a problem with your vehicle's secondary air injection system. The secondary air injection system pumps air into the engine's exhaust stream when the engine is cold and while decelerating. This allows the catalytic converter to heat up faster during a cold start, and while decelerating, adds air to the exhaust stream before the catalytic converter to better reduce emissions. The system operates via an air pump and a diverter valve, which controls whether air is delivered to the engine exhaust or the atmosphere; depending on the engine condition at any given moment. The entire purpose of the air injection system is to lower vehicle emissions. Injecting air into the exhaust stream leans out the unburned air/fuel mixture, causing the gases to burn hotter and reducing HC (hydrocarbon) and CO (carbon monoxide).
DTC P0411 indicates the engine control unit (ECU) has detected an air flow problem within the secondary air injection system. The trouble code is fairly vague, in that, it does not identify a particular defective air injection component and requires a hands-on diagnosis to determine the root P0411 fault. We should note however, the code is commonly due to an air injection diverter valve which is sticking due to carbon buildup. We recommend inspecting this component first. Other faults include, an open or shorted air pump or air pump wiring harness or connector, defective air injection control or diverter valve (as previously mentioned), or if the diverter valve is electronically controlled, the valve's solenoid and wiring harness and/or connector. Excessive carbon buildup within the air injection passages and/or disconnected or damaged air injection hose(s) will also trigger a P0411 trouble code.
To test the AIR Injection system the first thing you'll want to find out is whether the AIR injection pump is working or not. The test we describe applies to electronic smog pumps only. Belt driving air injection pumps are easy to tell if defective. Usually you'll hear something oddly wrong with the pump while it's spinning. Electrical pumps are almost as easy to detect malfunctioning, but because these pumps are fairly quite while running, you'll want to trigger the pump to run by bypassing its power supply and while the engine is turned off.
Once you're able to get the smog pump to run by bypassing it, you've ensured the fault is not with the pump. You may then move on to testing the air pump's electrical circuit. You know that the pump runs when applying direct power, now you want to know if the computer is supplying voltage to the pump itself. Once this is verified, you may inspect the diverter valve. Apply vacuum to the diverter valve (if vacuum controlled) in order to see if it is opening its air injection passage.
A visual overlook for obvious air injection system defects along with the tests above, should allow you to determine the root cuase of your P0411 problem and learn which parts need to be changed. The simplest repair would be cleaning out the AIR injection passages and diverter valve. The most costly repair would be having to replace the air injection pump.
As far as symptoms of P0411, most often you will not notice any problems except that of an illuminated Check Engine Light. Getting the check engine light to turn off will requiring clearing the P0411 trouble code from the ECU.
Step to take to get the p0411 problem fixed... Find the defective smog part, make the proper repair and reset the ECU. Once this is done, the check engine light will turn off. Your vehicle will then need to be driven for 200-300 miles (drive cycle) over the course of a few day and in both city and highway traffic conditions in order to set the AIR injection readiness monitor. Assuming the check engine light no longer turns on and the AIR injection readiness monitor status shows as completed, your vehicle will be ready to undergo the smog inspection. Using a scan tool, you'll be able to check when the AIR injection monitor is complete.