Circuit/System Description
WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
The remote control door lock receiver (RCDLR) sends the prerelease password to the engine control module (ECM) via the serial data circuit. The ECM then sends a challenge to the RCDLR. Both the ECM and RCDLR perform a calculation on this challenge. If the calculated response from the RCDLR equals the calculation performed by the ECM, the ECM will allow vehicle starting.