AIR [ Air injection system] has nothing to do with egr or pvc sytems/workings.
It is an Air Pump that bring auxillary air into the exhaust system during warm
up to limit nox and aid in fast cat warm up.
If a Secondary air system code is brought up, one want s to see if the pump
comes on during the first 2 min of cold operation.
The AIR system never works after the engine management goes into Closed Loop
control. When closed loop is attained , the ecu disconnects AIR.
If no operation of pump, checks in order are fuse, vac line to check valve ,
and AIR switch-over valve operation.
If pump does operate, then the code can relate to a faulty 02 sensor. If the
sensor does not see .o4mv [ real lean]when the ECU does a flow test, it will
bring up the AIR flow code..so . the 02 sensor has to be tested for Min
voltage reading limit to check out as OK.
This is the only time the 02 sensor is required to drop this lean, so a normal
o2 sensor fault code will not come up as bad sensor.
This test is best done by a Benz tech, as the o2 is seldom condemned by the
average mechanic, but is often the culprit for AIR Flow code on Benz EFI and
is also the first indication of a starting to fail sensor.