I have a 1995 c220 and I keep getting this code P0411. I would like some INFO on what to check. I have checked the Vacuum lines and the replaced the purge valve. I know it is in the emmissions but I am stumped as where to look next. What should I check Next ? Thanks in advance.

P0411 - secondary air injection flow too low.

This is an easy system to test with a proper scanner. In activations the air pump is turned on and the O2 sensor voltage must go below 40mv in a short time. The typical problems involve the vacuum control of the airpump check valve, the air pump itself, the circuit to the air pump and the O2 sensor itself. This is not usually a piping problem.

The things you can do are to watch for the air pump working on a cold start and verify that the vacuum is reaching the check valve at that point and proceed from there.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I had this code, I checked out the secondary air injection pump and it was functioning normally, pumps ran, vaccuum powered valve worked. This error is reported to ECU by #1 oxygen sensor which I replaced and the light never came back, car starts easier now when hot. $99.00 part at partsshop

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1995 c220 (harness issues sold)
1999 clk 320 cabriolet