Fix P0492: Mechanic’s solutions that WORKED

The code P0492: Secondary Air Injection System Insufficient Flow (Bank 2) indicates a fault in the Secondary Air Injection System, specifically an insufficient flow on Bank 2. This issue is most commonly caused by a faulty air injection pump, damaged hoses, or a malfunctioning solenoid.

P0492 quick overview

Meaning	P0492: Secondary Air Injection System Insufficient Flow (Bank 2)
Is it serious?	Yes, it can affect emissions and potentially engine performance.
Possible causes	– Faulty secondary air injection pump – Damaged air injection hoses or connections – Faulty secondary air injection solenoid – Leaking, stuck, or blocked combination valves – Vacuum leaks in the secondary air injection system – Clogged passages in the exhaust manifold – Faulty check valve in the vacuum system
How to diagnose?	Scan for Codes: Confirm P0492 using an OBD-II scanner. Visual Inspection: Check for damaged hoses and connections in the air injection system. Pump Test: Verify the operation of the secondary air injection pump. Solenoid Test: Check the secondary air injection solenoid for proper operation. Check Valves: Inspect and test the combination valves for leaks or blockages. Vacuum Test: Ensure there are no vacuum leaks in the system. Exhaust Manifold Inspection: Check for clogged passages in the exhaust manifold. Check Valve Inspection: Verify the function of the check valve in the vacuum system

Code P0492 pops up when there’s a problem with the extra air the car pumps into the exhaust system to reduce emissions. If this system isn’t working right, it can’t add enough air, usually because something is blocked, broken, or leaking. This needs to be fixed because it can lead to higher pollution and sometimes affect how the car runs.

How to fix P0492 – learn from mechanics

I looked into P0492 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: Porsche

Vehicle Information 2004 Porsche Boxster S 3.2L

Issue + Repair History

• MIL (Malfunction Indicator Lamp) on
• Codes: P0491 (secondary air below limit), P0492
• Secondary air faults, tested air pump and valves

What Are People Suggesting to Fix Issue

• Check for plastic lines on top of engine for damage or disconnection
• Inspect for diverter valve sticking issues
• Manually apply vacuum to diverter valve and observe O2 sensor changes
• Command secondary air pump on for further diagnostics

What Was the Final Fix

• Found cracked headers, replacing catalytic converters fixed the problem
• Used magnehelic gauge to test for clogged head ports, indicating ports were okay

Case #2: BMW

Vehicle Information
2003 BMW 325i 2.5L

Issue + Repair History

• MIL (Malfunction Indicator Lamp) on
• Codes: P0491 (air injection flow), P0492 (air injection bank 2)
• Previous repairs: Main hose replaced, vacuum hose to valve replaced, crankcase and intake boot replaced

What Are People Suggesting to Fix Issue

• Replace the non-return valve at the front of the cylinder head

What Was the Final Fix

• Valve removed and inspected, found rubber pieces coming apart and valve not opening. Replacing the valve fixed the problem

Case #3: Volkswagen

Vehicle Information
2005 Volkswagen Touareg 4.2L

Issue + Repair History

• MIL on
• Code: P0492 (air injection malfunction bank 2)
• Replaced check valve on bank 2

What Are People Suggesting to Fix Issue

• Check for a broken intake flap arm at the front side of the intake
• Check air injection lines again, especially near the passenger side of the engine compartment near the brake vacuum pump

What Was the Final Fix

• The issue was a broken intake runner diaphragm. Replacing it resolved the problem.

Case #4: Audi

Vehicle Information
2008 Audi Q7 Premium 4.2L

Issue + Repair History

• MIL on
• Codes: P0491, P0492 (Secondary Air Injection System Insufficient Flow)
• Replaced secondary air injection pump and secondary air MAP sensor
• Found check valve to solenoids installed backwards

What Are People Suggesting to Fix Issue

• Ensure the Secondary Air Injection (SAI) runs in a two-part sequence: first, the solenoids/valves should open allowing air to flow into the exhaust; second, the valves should close and “dead head” the pump

What Was the Final Fix

• The issue was resolved by correcting the installation of the check valve to the solenoids, ensuring they were getting vacuum.

Case #5: Audi

Vehicle Information
2011 Audi A8 Quattro 4.2L

Issue + Repair History

• MIL on
• Codes: P0491, P0492 (Secondary Air Insufficient Flow)
• Tested SAI pump, solenoids, combi valves, vacuum system; found no leaks
• TSB for 3.2 and 3.0V6 about clogged passages noted but this engine not listed

What Are People Suggesting to Fix Issue

• Check vacuum system thoroughly, ensuring no leaks
• If vacuum holds for 10 minutes, consider replacing combi valves with updated parts
• Inspect and clear SAI holes in the engine head surface if necessary

What Was the Final Fix

• The issue was resolved by replacing a faulty check valve, which was not holding vacuum for the required duration. Once replaced, the monitors ran successfully and the issue was resolved.

Common Advice	Brief Description of Diagnostic Step
Check Vacuum System	Ensure there are no leaks in the vacuum system. Apply vacuum at the check valve and ensure it holds for a specified duration (e.g., 10 minutes).
Inspect and Test SAI Pump and Valves	Verify the operation of the secondary air injection pump and solenoids. Test the combi valves for proper opening, closing, and holding vacuum.
Smoke Test for Leaks	Perform a smoke test on the system to identify any potential leaks that might not be easily visible.
Check for Clogged Passages	Inspect the secondary air injection passages in the exhaust manifold and engine head. Clear any blockages found.
Verify Electrical Connections	Ensure that power and ground connections to the pump are intact and that solenoids are receiving the correct signals.
Replace Faulty Components	If a specific faulty component is identified (e.g., check valve, combi valve), replace it with new or updated parts.
Monitor System Operation	Run readiness tests and observe the operation of the system during the test, particularly the response of solenoids and valves.