Hello All, first post first Benz. I'm attempting to check the duty cycle as I've had to replace a leaking EHA valve. After a while I determined my year has to be in a diagnostic mode to get the reading at the connector.

According to a footnote in service info I've seen, not only does it need to be in this mode. It also states that the check engine light must not be on. Now I hate to sound stupid, is it referring to when engine is running while checking duty cycle or to KOEO ? If the latter how does one achieve this ?

It's referring to CEL engine running only, it always comes on at KOEO.

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1991 300E - 212K and rising fast...