Key fob not detected after key battery change

[Lexusls43o]

Hi guys,

 

Dash was telling me my key fob battery was low so got it changed. Since then the smart key is mot working. Any ideas on how to sort it out? 

The buttons on the fob work lock/unlock/trunk. When starting the car it says key fob not detected. It will start with the key in the ignition. Tried the button below the dash for the smart key. Smart key light does flash green along with the red light next to it. 

 

Any help would be appreciated. 

[dcfish]

OK, First check the battery in the fob to make sure it is good, Now if it is good (new) Disconnect the neg. battery terminal for 10 minutes...Reconnect and start the car,,,

[Lexusls43o]

Going to check the battery first. Tried the disconnecting neg terminal on the battery to no avail