Auto Systems and Repair: P0411 - OBD-II Trouble Code
OBD II Fault Code
- OBD II P0411
Fault Code Definition
- Secondary Air Injection Incorrect Flow Detected
The Secondary Air System pumps outside fresh air into the Exhaust System during cold engine start up. This additional air helps burn up the very rich exhaust emissions that are produced when the engine is warming up. The Secondary Air System typically has an Air Pump, some tubes or plumbing to route the air and Air Management Valve(s) to control the air flow.
- Check Engine Light will illuminate
- In many cases, no abnormal symptoms may be noticed
- In some cases, the engine may hesitate on acceleration
Common Problems That Trigger the P0411 Code
- Defective Air Management Valve(s)
- Faulty Air Pump or Air Pump Relay
- Faulty air control solenoids or vacuum lines
- System may be restricted or plugged with carbon
- Air Managment Valve(s) functions, but is slightly restricted
- Air Pump is replaced when the relay is the problem
- Parts are replaced when the the system is restricted or plugged with carbon
- Many vehicles set a code P0411 due to restricted Secondary Air Management Valves
- Study the Diagnostic Theory section below to learn about the scan tool data that indicates defective Air Management Valves and the advised replacement procedure
- Learn more in the Diagnostic/Theory section at the bottom of this article
P0411 Diagnostic theory for Shops and Technicians
When a code P0411 is set, the PCM is not seeing the front oxygen sensor voltage drop sufficiently when the Air Pump is supposed to be adding outside air in to the exhaust system to burn off the excessive HCs and CO that are created during the cold start of an engine. One should test the system with a data streaming scan tool, during a stone cold start up of the engine. Some scan tools provide the Technician methods to test the Secondary Air System or SAS when the vehicle is already warmed up, but this feature is not present on all scan tools.
Cold start the vehicle and watch the front oxygen sensor(s) on the scan tool data stream. After about 5-10 seconds, you should hear the secondary air pump start, it actually sounds like a vacuum cleaner running under the hood. Just as the Air Pump kicks in, the front oxygen sensor(s) voltage should go to less than .125 volts ( 125 millivolts ). If this does not happen, then you have verified a fault condition in the SAS or Secondary Air System.
- If you do not hear the Air Pump Motor start, then check the SAS Air Pump and relay.
- If you hear the motor, inspect the components that control the Air delivery such as the Air Management Valve Solenoid, the Air Management Valve and the rubber hoses, metal piping and passages.
- On V6 or V8 vehicles, if BOTH front oxygen sensors do not drop to below .125 volts or ( 125 millivolts ) then blow into the Air Management Valve(s). The valve or valves should flow very evenly.
- NOTE: you must replace the check valves as a set or the code will keep re-setting on GM vehicles, because the PCM needs to see an EVEN drop of the front oxygen sensor voltage.