So a few weeks ago i lost volume control in my 2015 IS 350 with the mark levinson sound system.. I took to lexus they thought was amp but werent sure, I went to a local car audio shop and they said it was amp.. So i bought a refurbished amp online and just installed it.. Still no volume control... I called the gtuy who sold me amp and he went over a few tests with me using multimeter on the amp connection cables and everything tested out fine..

Im lost at what to do.. my next guess would be head unit, but everything else on the head unit works.. all the other switches and everything are good.. i dk what else the issue could be... Can anyone help me??

 

While amp failure on the ML system is not common, I guess anything is possible.
Usually it's the 2014 non-ML that has no sound and an Amp fixes the issue.

Since you said you had a multimeter, I've attached 2 docs that might help you out.
The first shows you how to check for codes that may be related to the Amp.
The other one shows you what the readings should be at the Amp itself under normal operation...ideally you would only be checking for Power and Ground where it indicates since you have no sound from the speakers (the waveform checks would be pointless).
While it's hard to imagine you have 2 bad amps...your original and the replacement...it's likely then something in the Amp circuit.

If you find anything out of the ordinary, post back and we can help further.