1996 W202 CEL-p0411
 

So what usually cause a P0411 CEL code

Secondary air injection system, incorrect flow

the car got 198k miles on it

i was able to reset the CEL and it hasnt come on since

what should i check for??

TIA

PS the sec air inj is working fine (i can hear it during when its cold start)

If I understand this correctly, during " secondary air injection ", the ECU is monitoring the oxygen sensor output, looking for a " lean " signal.
I would back-probe the O2 sensor & observe the voltage reading during & after secondary air injection. ;)

C220 or C280?

Gilly

its a C280