The air injection is an emission catalyst "warm-up" system.

The way ODB2 checks the system for correct operation is by engaging the system at idle when the engine is hot. At that point the front O2 sensors must respond by dropping their output voltage to less than 40Mv & keeping it at that point while the test runs.

MOST common problem is broken vacuum lines to 1 OR both of the diverter valves, OR a bad air pump relay or fuse. DOES the pump run on a cold start??

MOST dedicated MB scanners can perform that test & show results.

ON many M112 engines the air injection ports in the LEFT cylinder head plug up with carbon. Head removal is required for that malfunction.

One way for you to see if that is the problem is to remove the diverter valve & start the engine & see if exhaust comes out of that port.

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