arthurchapin

Hi, i have a 2002 w463 that won’t engage the diff locks. The symptoms are as follows:
1. When the center lock is activated the pump runs continuously but never engages (no red light). The front and rear do the same although I don’t believe they can be engaged if the center isn’t.
2. The car occasionally has a TC in neutral error, this happens when the door is ajar and running without the parking break on (odd combo). I recently had the TC motor replaced but at the time did not know about the TC ECU that likely should be replaced as well?

I recently brought it to a new shop and they have spent a while trying to fix the diff lock issues, what I don’t understand is they say the problem isn’t the vacuum system and they think it’s with the front locker and have said they are doing detailed pin testing, this doesn’t make sense to me as I thought the locking system was all mechanical and if the vacuum system is fine what are they testing? They made it sound like it was electrical?

so three questions?
-Could the TC in neutral error be causing this, I know in later model Gs that the TC needs to be in Low but that wasn’t true in mine. The little H/L logo is a blank square now but has been that way for a while.
-Is there a scenario that the vacuum pump can run continuously but the vacuum system is fine?
-Lastly, would anything to do with the front locker other than a leak in the vacuum system prevent the center diff from locking?

any help or advice would be greatly appreciated.
thanks!
Arthur