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 engine control module (ECM) has 3 5-volt reference circuits. The ECM provides the 5-volt reference to various sensors. Each reference circuit provides a 5-volt reference for greater than one sensor. An open, short to ground, or short voltage on one of the 5-volt reference circuits can affect all the components connected to that 5-volt reference circuit. The ECM monitors the voltage on the 5-volt reference circuits.