Fix P0411: Mechanic’s solutions that WORKED

The code P0411, which stands for “Secondary Air Injection System Incorrect Flow Detected,” is generally not a serious issue but can impact emissions and fuel efficiency. This code can be caused by various factors, including vacuum supply problems, O2 sensor issues, and internal leaks in check valves.

P0411 quick overview

Meaning	P0411: Secondary Air Injection System Incorrect Flow Detected
Is it serious?	Typically not serious, but may affect emissions and fuel efficiency.
Possible causes	– Vacuum supply problems, blocked lines, or faulty check valve. – Internal leaks in check valves. – O2 sensor problems – Ground issues – Turbo bypass valve with internal leaks. – Malfunctioning solenoid valve controlling vacuum to kombi valve. – Failed combination valve. – Turbo over-run valve damage or blowing.
How to diagnose?	1. Investigate vacuum supply issues, checking for blockages and the check valve’s functionality. 2. Inspect check valves for internal leaks that could set the code. 3. Temporarily block air pump hoses and retest while considering O2 sensor or ground issues. 4. Examine fuel trim strategy and O2 sensor behavior. 5. Use a vacuum pump to check the turbo bypass valve for internal leaks.
What is Secondary air injection?	Secondary air injection is a system in a car that injects fresh air into the exhaust to help reduce harmful emissions during cold starts.

How to fix P0411 – learn from mechanics

I looked into P0411 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Volkswagen

Vehicle Information:

• Make: 2000 Volkswagen Beetle
• Model: GLS
• Year: 1.8L

Issue + Repair History:

• MIL Lamp on
• Fault Code: po411 (Secondary Air Injector Incorrect Flow)
• Vacuum issue at 2nd air injection solenoid
• Combination valve replaced
• Vacuum leak at turbo bypass valve causing po411 code

Other OBD2 Codes + Test Results:

• po139 (Oxygen Sensor Circuit Slow Response Bank 1 Sensor 2)
• p1118 (Man. Controlled Fuel And Air Metering)
• p1198 (Man. Controlled Fuel And Air Metering)
• p1432 (Man. Controlled Auxiliary emission controls)

Suggestions to Fix Issue:

1. Check the turbo bypass valve with a vacuum pump for internal leaks.
2. Use VAG-COM to run output tests on the solenoid valve controlling vacuum to the kombi valve.
3. Consult Identifix for a detailed procedure to diagnose po411.
4. Consider a possible failed combination valve as a common problem per Anthony Kandarapally.
5. Investigate the turbo over-run valve for a blown condition, as per David DeLeon’s suggestion.

Final Fix:
The final fix was identifying a leaking turbo bypass valve, which was robbing vacuum from the 2nd air injection solenoid, causing the po411 code.

Case #2: Ford

Vehicle Information:

• Make: 1996 Ford F-150 Eddie Bauer
• Engine: 5.0L

Issue + Repair History:

• MIL Lamp on
• Code P0411 (CA emissions vehicle)
• Secondary air injection system issue
• Code sets intermittently
• Checked all components and found nothing wrong initially
• Freeze frame data indicated secondary air injection might be stuck on
• Removed and tested bypass valve and AIRB valve (vacuum switching valve), both seemed fine
• Manually diverted air to the heads and both O2 sensors responded immediately
• No vacuum leaks found in hoses

Suggestions to Fix Issue:

1. Check for internal leaks in check valves as they can set the code.
2. Block off air pump hoses and retest, consider bad O2 sensors or ground issues.
3. Consider the possibility of the code setting due to fuel trim strategy and O2 sensor behavior.

Final Fix:
The issue was resolved by disconnecting the battery and resetting the Keep-Alive Memory (KAM) and fuel strategy. After resetting, the vehicle’s fuel trims stayed within a normal range, and the P0411 code did not return. This fix was discovered after thorough testing of all components and understanding the impact of the fuel trim strategy on the code.

Case #3: Cadillac

Vehicle Information:

• Make: 1997 Cadillac Catera
• Engine: 3.0L

Issue + Repair History:

• MIL Lamp on
• Codes: P0411 (air), P0507 (idle control)
• Car previously came in with P0411 code, check engine light on
• Checked bulletins and replaced check valve
• The next day, the check engine light came on again
• Currently, P0411 and P0507 codes are both set
• Air pump shows signs of water stains and has an acid leak, but it’s working

Suggestions to Fix Issue:

• Investigate vacuum supply problem, as one of the lines connected to the check valve was plugged, and the check valve was not functioning correctly (Fixed P0411).
• Consider that P0507 (idle control) may have set during diagnostics or as a result of the real problem.
• Clear the codes (record any freeze frame data first) to see if they come back immediately.

Final Fix:
The issue was resolved by identifying a vacuum supply problem, specifically a plugged line connected to the check valve. This issue was causing the P0411 code. After cutting the end of the check valve, reconnecting the vacuum line, and resetting the code, the problem was resolved, and there were no further issues for three weeks (Fixed P0411). P0507 (idle control) may have been a secondary issue and may have set during diagnostics or as a result of the initial problem.

Case #4: BMW

Vehicle Information:

• 2005 BMW 325i 2.5L

Issue + Repair History:

• MIL Lamp illuminated
• Computer Codes: P0411- Cold air injection problem
• Manifold Vacuum Readings: Idle – 21 in., Cruise – 21 in.
• No past repair history mentioned

Other OBD2 Codes + Test Results:

• No additional OBD2 codes or test results noted

Community Suggestions to Resolve Issue:

• Suggested testing the air pump for operation and inspecting vacuum lines and the valve.
• Mentioned a possible Technical Service Bulletin (TSB) about reversed wires on the secondary pump’s connector, though unsure if relevant to the 2005 model.
• Advised checking the valve and air pump for proper function, looking for clogs or leaks in the valve or hose.
• Recommended performing a test plan for comprehensive diagnostic information.

Final Fix:

• The issue was resolved by addressing the sticking closed cold air injection valve.

Case #5: Audi

Vehicle Information:

• 1998 Audi A6 Quattro 2.8L

Issue + Repair History:

• Poor Idle Quality, Misfire, MIL Lamp on
• Computer Codes: P0411- Secondary air injection system
• Replaced secondary air solenoid, valves, and relay due to air valve leakage.
• Occasional code occurrence, mostly after highway driving.
• Rough running and MIL light illumination after exiting the highway.
• Resets and runs fine after P0411 code sets.

Other OBD2 Codes + Test Results:

• No additional OBD2 codes or test results mentioned.

Community Suggestions to Resolve Issue:

• Suggested checking vacuum lines and crankcase breather hoses. Test combi valves, ensure they hold vacuum, and check secondary air hose from the air pump. Mentioned a possible issue with the front O2 sensor.
• Advised checking all vacuum hoses for leaks.
• Recommended thoroughly inspecting vacuum lines and checking for ruptures, especially the brake booster line.

Final Fix:

• The issue was resolved by fixing a failing coolant temperature sensor, which caused it to read extremely low (-40) for 8 to 10 seconds. This triggered the secondary air system (P0411) but did not set a code for the Engine Coolant Temperature (ECT) sensor.