System Block Diagram
The source of diagnostics commands for immobilizer equipped BCM's is different depending upon the type of immobilizer used. The diagnostics communication for the SMARTRA system will be performed by communicating with the ECM on its K line.
In the case of a BCM that has an immobilizer, the detection of a tester being present will cause the K-line enable relay to close and the Diag. pull up to be switched off. This mode of the diagnostics interface is called "Diagnostics" mode. This will then remain the case until the tester is disconnected. When the K-line enable relay is off and the diag pull up is enabled, this mode is called "immobilizer" mode.