Million Dollar Question

I’ve been struggling for a while now with this, not sure if all trucks do it but on my 386 with a ISX15, when you turn the ignition to the on position, the truck starts the Systems check, now during the systems check it releases little bursts of air and one significant burst at the end of systems check.

Does anybody know what valve controls the last burst? I’ve asked the dealer and several mechanics and nobody knows .

 

Yes does it regardless and it sounds like it’s coming from driver side air tanks area

 

That’s what I thought but I recently had my clutch changed and they said it’s not likely trans is a Eaton 10 speed