I'm about to take possession of a 2001 ML55. I bought it from my indie mechanic and it's ready to go, except he's having trouble getting it to pass inspection.
It won't get past these two monitors- secondary air pump and the evap system.
He's been working on German cars for over 30 years, so he knows what he's doing and this has him stumped.
He's tried every trick in the book and still no go. It only has to pass one more for him to put an inspection sticker on it.
I thought one of you might have had the same issue.
Thanks for any suggestions you might have.

Secondary air pump should be pretty straightforward to diagnose I would think. I believe SAI pump should come on when the vehicle first starts up to help the catalytic converter deal with rich AFR mixtures that are necessary to start the engine when cold.

EVAP system will probably need a smoke machine to check for leaks. On a 20+ year old truck I’m sure there’s a crack in a hose or some other air leak holding you up.

Good luck! 👍

Thanks. I sent your idea on checking the evap for leaks to my mechanic.
He replied that there are no faults for anything. He also said "The problem is that the monitors won't set for the evap and secondary air".

Correct…and usually the reason the monitors won’t set is because there is a problem with those systems lol…. There is also the possibility that he is not hitting the necessary data points that the ECM is looking for to complete the drive cycle. It’s not as simple as “Get in and drive car”…. Here’s an example of a typical drive cycle check list: https://www.nyvip.org/PublicSite/OBD...ive-cycle.html So if you don’t hit those particular temps/times/speeds, then the drive cycle will not complete and your monitors will show as “not ready”.

Thanks. I'll pass that along.

Passed inspection. I pick it up tomorrow.

Great! So, what was the thing hanging it up? Did he just drive it some more?

He reran the test first thing in the morning after a cold night and the monitors reset.
Good thing too. He left for vacation after work yesterday. If it didn't pass, I would have to have waited at least another week.

Ah, makes sense. I know at least the evap system test needs to happen on a cold start so that makes sense. Great news! 👍