The VIU voltage is supplied through three fuses; the SEO IGN fuse in the fuse block, the SEO1 fuse in the engine wiring harness junction block and through the retained accessory power (RAP) system. The VIU is grounded to G203. The VIU is capable of controlling the systems when commanded to do so by the OnStar® Call Center.

The VIU controls the inflatable restraint sensing and diagnostic module, locks, horn, theft alarm and the headlamps through class 2 communications. The VIU also interfaces and communicates with the radio through the diagnostic signal entertainment and comfort bus. The OnStar® audio is played through the radio on the remote radio right audio signal circuit, the remote radio left audio signal circuit and the remote radio audio output (-) circuit. The global position system (GPS) antenna is connected to the VIU.

The VCU is supplied power from the vehicle interface unit (VIU) through the XCVR BATT and the XCVR IGN circuit. The VCU is grounded through the XCVR DIG GND circuit to the VIU. The cellular antenna connects to the VCU. The VCU uses a three wire bus to communicate with the VIU. This three wire bus is a dedicated communication line between the VCU and the VIU. The audio commutations are made to the VCU through the VIU.

The button assembly is fed power from the VIU through the keypad power circuit. It is grounded with the keypad GND circuit to the VIU. All three button assembly signal and return circuits go to the VIU.