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what aftermarket equipment have you installed?was the issue there prior to changing equipment?
IF that is all that was installed (no change of tires or rims, no tinted windows, etc) then the best way to proceed is to remove the obvious head units that can be seen.You do not have to remove or disconnect wiring, just the components & have the Dealer / Service Manager recheck the system, being sure to tell them the issue was there when you purchased the vehicle.There is no way anyone here can tell you IF all the Aftermarket Equipment was installed correctly, so this would come down to wiring & any Signal that would be overriding the Tire Pressure Monitor System........which I have seen with Police Radios & CB's.....(frequency Interference)Sorry.......I am not able to callWe can continue here..........
I have been installing, designing & repairing Aftermarket Radios, Remote Starts, two way Radios, etc. for over 30 years.......Just because it was installed by a "certified installer" does NOT make the installation "fool proof"........people make mistakes.........That said, you posted that the issue was there prior to anything being installed, which makes it a "Toyota problem".IF the Service Manager was no help, go to another DealerIF there is no other Dealer close, contact Toyota Customer Service & get them to authorize the Dealer.IF that is not good enough, then there is no creditable answer that you will accept.Stands to figure that if the issue was there prior & you do not want to remove the equipment to prove to the Dealer that it is nothing you have done, then you will be stuck with the problem.Good Luck