What activates the air injection pump and what deactivates it? I've got a situation where upon starting the engine, the air pump runs longer than normal, 90-120 sec, vs 30 secs. In addition, which I think has caused a couple of P0411 CEL the past couple weeks, when the air pump comes on the second time around (after about 5 min of drive time) it has been abruptly (i.e., not smoothly) shutting off after 1 or 1.5 sec versus 5 secs or so (and shutting off smoothly). Anybody know what this might indicate? Some kind of switchover problem, O2 sensor problem, or air injection pump problem? Thanks.

On cold starts the air pump running duration is TEMP dependent, ie; the colder the engine is the longer the pump should run. The second running is ONLY for diagnostic purposes. Should run aprox 10-15 seconds to check the system. MB scanners can activate that system & a good technician can diagnose the results.

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Thanks MB Doc. Does it point to the/a cause of the P0411, secondary air injection failure, if the diagnostic (i.e., not initial) activations of the air injection pump seem to run for only <3 seconds and stopping very abruptly? Is there impending failure on some part, as this doesn't happen every time. I've gone 6 days without the CEL re-lighting but expect that once enough faults accumulate it will come up.

Somewhat subjective question!

With-out seeing scanner results that could only be a guess!
Either the pump is asking for too much current from relay or the relay stops supplying current or the engine temp is too low OR the front O2 sensor is defective OR OR OR..........

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator