Question about 1996 Mercedes-Benz Mercedes Benz S Class Coupe

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I have a 1996 Mercedes S 320 secondary air pump

I have a 1996 Mercedes S 320 that throws code po411 secondary air injection system, incorrect flow. I clear the code and it takes anyware from 1 day to a month or so to come back on. My understanding is the pump comes on when the engine is cold and then shuts off. But the light will come on driving down the road after being warmed up.
So I'm wondering how to repair the pump and or how to remove it to repair it. Seems like an intermitant problem since it takes differant amounts of time to throw the code. Anyway it has me confussed

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Hello I'm an M.B. tech- lot's of people have had dificulty with that code. The code means just what it means insuficiant air flow. The egr system does the same thing. What generaly ends up being the problem is a clogged port in the engine head. Unfortunatly on the air pump the port is near the exhaust side of the deck and you must remove the head to repair it where as the egr you can clean the port at the throttle motor. First thing you need to do is make sure there are no more codes in the system. The way that the ecu moniters the operation of the air pump is map senser for vac to the switcthover valve which is the same switch over valve for the egr located in the front of the cam cover. Next it will use the front o2s to moniter the airflow. Also it moniters the airpump relay operation. Operation is started during open loop by the coolant temp. senser. I beleive that this vehicle could possibly have a diagnostic mod along with the engine ecu which moniters the ecu performance. This also needs to be scanned for codes, They discontinued these in late 95. Make sure you have source vac, to the switchover valve-next moniter switchover valve otlet to diverter valve during air pump operation. To properly moniter o2 sensers you will need the proper equipment. Inspect all the airpump plumming as well. assuming the air pump is getting power and operating properly. I would recommend taking the vehicle to an M.B. repair shop and have the system function tested and scanned-with a flow check for the clogged air injection ports. Depending on how many miles I would just do a valve job. If you have any more questions just post and I will get back to you

Posted on May 25, 2009

  • abraham_sark Mar 14, 2015

    Everything seems to be working fine, I took the valve out from the exhaust and ran chemicals to clean carbon, I replaced the air pump and switchover valve plus the purge valve, I cleared all hoses and checked vacume hoses are fine, I started the car the relay and pump worked fine, I checked for vacume at the valve by the exhaust and there was a vacume. I ran my scanner again through 38 pin no codes found what so ever, I ran my scanner again from OBD2 and found no codes what so ever. Everything is working fine everything is ready on the monitor only secondary air system not ready. I d

  • abraham_sark Mar 14, 2015

    No check engine on, car running smooth at idle and driving fine, no codes found but still the secondary air system not ready not sure what else to do to be honest.


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I have a 1998 Mercedes S320 everything is reading ready for smog test except the secondary air injection.

1- The air pump works fine I jump started it and it works fine. I also felt it working when I started the car in the morning but once I disconnected the large hose from the air pump it stopped working.
2- the relay is fine too I replaced it as well. When car is worm and running I get no readings from the pump connector what so ever but the relay is
3- all fuses are fine I cheked them one at the time.
What else it could be I wonder any help will be appreciated.

Posted on Mar 13, 2015


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