IBU (SMK + BCM + TPMS) & PCM (ECM/TCM) Control Module (SMARTRA Error)
WARNING: This page is about a different car, the 2020 Hyundai Santa Fe. However, it is still accessible from the selected car via links, so may be relevant.
When turning the ignition switch ON or cranking the engine, the engine ECM begins communication with the IBU (SMK + BCM + TPMS) by sending a VIN (Vehicle Identification Number) request signal to control the engine in a stable manner.
The IBU (SMK + BCM + TPMS) sends an "Ignition Approval Not Possible" signal to the engine ECM when the Immobilizer cannot function. In this case, the engine ECM enters an ignition inhibition state and a driver cannot start the engine (ignition or fuel injection inhibited).
On the other hand, the IBU (SMK + BCM + TPMS) sends an "Ignition Approval" signal to the engine ECM including the VIN and learnt status information when the Immobilizer can function.