So I have been running into the perpetual P0410 code on my ML320 for the last year or so and continue to look for a solution.

• I have cleaned the manifold/hoses from top to bottom
• Eliminated possible vacuum leaks with smoke test
• Replaced the EGR
• Replaced the Secondary Air Pump.
• Cleaned the Air-Injection Check Valves and ports
• Replaced the Air Injection Control Valve
• Replaced the gasket around the intake pipe at the manifold opening and MAF.

I am starting to believe the issue is with our M112 and M113 Air-Injection Check Valves. Has anybody found a replacement or upgrade for these? It seems like these were poorly engineered and collect a lot of soot at the reeds, inside the openings and the check valve bell. It would be nice to find an upgrade to completely replace these.

TIA
Eric

One, or both of the upstream O2 sensors could be the problem. The sensor voltage should quickly drop to <100mV when the pump is running.....assuming the rest of the components are working. The system is pretty simple but you need to be able to look at some live data to figure it out.

When you say you cleaned the ports did you clean all the passages in the cylinder heads? What I have seen is the passages through the cylinder heads get stopped up and don't allow the air to be injected into the exhaust flow as designed. It usually requires cylinder head removal and sending them to a machine shop to be cleaned via long drill bits and solvent soaking tanks.

Like the previous post says though is you need to be able to monitor front O2 sensor values with the system operating and the values should drop quickly when the pump comes on.

__________________
Mercedes Benz Master Tech - Retired

The quickest way to check the sensors (assuming you can monitor the voltage) is to hold the RPM at 2000-2500, at operating temp. Quickly stab the throttle to the floor and then lift. This will activate the decel/shutoff causing a temporary lean condition. If the sensors aren't "lazy" the voltage will drop like a rock....

Thanks ILUVMILS and RPM55. I believe I have cleaned out all of the possible ports in the manifold leading to hoses and the ports leading to the check valves (in the cylinder heads). So I believe this issue is illiminated.

I also replaced Bank 1 and 2 upstream O2 Sensors, which I did not mention above. However, I have not perfromed the tests ILUVMILS describes above. I will try this and get back to you. Thanks for the help!

ISSUE SOLVED: Finally spent the money on a smoke machine and well worth every penny ($150 w/smoke juice). After a year of running around with a check engine light on for a secondary air injection code, I immediately located what was causing my issue as soon as I hooked it up. It was the brake booster vacuum line connection that connects at the back of the manifold. There is a little plastic hose line connector that goes inside the manifold hole. I purchased mine here on Pelican. The original one was leaking like a civ. The one-way valve on the line may have also been plugged so I replaced the entire line as well. The smoke machine is the hero here on this one. I should have bought it a year ago.

It's crazy because I paid a garage to provide a smoke test about a year ago and he found nothing. I think this story shows it pays to do it yourself.