2008 Toyota Truck Tundra 4WD V8-5.7L (3UR-FE) 4x4 high / low light flashing

First off a shout out from churchill MB to paul and the mods and committed members for doing a great job here.. i don't ask to much help usually but this one is bugging me. customer of mine from NATURE 1ST TOURS brought in his truck . and said that he started the truck one day and the 4x4 hi lo started flashing continuously. ask about the previous drive it had made with weather and if it was though water . stuff like that. normal drive day dry conditions 4x4 was not even used that day he said. lights were not on when vehicle was turned off. so i did my diagnosing checked the 4WD CONTROL ECU the switch on dash . everything seems to be in check . resistance checks on 4x4 ecu canh and canl seem in range the ig wire seemed to have the rite voltage and ground was it order as well. by the way this is the floor mounted shift type. can here a distinctive tone from the from the a.d.d actuator . like its playing a song. not a consistent flat tone. anyone have come across this issue let me no or any suggestions. i'm not throwing parts at it. not my style. thanks

Just going from memory, I think the motor in the a.d.d actuator is just normal - two wires that reverse polarity, like a power window motor. Should be easy to check that. A wiring diagram is your friend there. There's also a switch on there for the position it's in. Those a.d.d.'s do fail.

Any codes in the 4WD module? Like John said, I've known the ADD's to fail. The seals go bad and the internals get loaded up with mud/water/junk. I see there was no weather immediately before the problem, but the internals could be corroded anyway.

restarted my tests from scratch , all pointed to the switch. there was no codes. related to this issue , just anti theft codes . and low catalyst efficiency . just waiting for for part to arrive . let you know once I have it installed . thanks fam