Secondary Air Injection

[Rod Spohn]

OK I have a 1996 Mercedes S320 with an automatic transmission with 177k miles on it. Over the last several years I have been getting the check engine light coming on. The code that comes up is P0411 Secondary air flow. I'll clear the code and it will come back on at different intervals. Sometimes it returns in a few days sometimes it takes weeks. I have checked more closely lately – once 265 miles between then 60 miles, the last time 195 miles. So it’s very random. I have been told the Secondary air system pump comes on when the motor is cold to help with warm up. But many of the times it will come on after the car has been running quite a while. Driving down the road and the light will come on, or sitting at a light it will come on. At first I thought it was when I let up on the gas but trying to pay more attention to how and when I’m now thinking that is not the case. I have taken the hose off the electric pump side and where it goes into the engine and cleaned what little carbon seemed to be there. And that didn’t seem to make a change and there was very little there anyway. So my question(s) is. Does anyone have any ideas what to do next? Does anyone have a procedure for removing the pump and or testing it. Being the pump is quite costly I want to be fairly sure that is the problem before buying a new one. I have seen used ones for sale for a good price but most come off cars that have quite a few miles on them so not sure that’s a good idea and also could use test procedures to check the used one if I go that way. I have always kept everything repaired as I’ve had problems but this one has kept me guessing. Any help would be awesome and appreciated. Thank Rod

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[brakel8]

The usual cause is a clogged air injection tube towards the throttle actuator. Either clean out the tube or replace it.

[fixbenz]

i would check the vacuum lines, from the intake to transducer, and to the egr itself, most of the time the vacuum line gets brittle (remove the cover to access the spark plugs, theres a vacuum line that runs in that valley too) you may have a broken vacuum line, i would go that route first. i have seen this problem several times!!

[Gullwing]

hook up 12volts to the pump, if it comes on that is not the problem. I think the problem is more in the EGR system, I have seen several M111 engines with P0411 codes because of the EGR.

[jagass]

Your air injection tube is clogged...Try to clean it...

[Rod Spohn]

Originally Posted by fixbenz

i would check the vacuum lines, from the intake to transducer, and to the egr itself, most of the time the vacuum line gets brittle (remove the cover to access the spark plugs, theres a vacuum line that runs in that valley too) you may have a broken vacuum line, i would go that route first. i have seen this problem several times!!

I have to thank you - I looked over the lines and found a break. I spliced and it's bee over 300 miles since fix and no light yet.