Circuit/System Description
WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The engine control module (ECM) has a 5-volt reference buss for each 5-volt reference circuit. The circuits are called 5-volt reference 1 and 5-volt reference 2. Each bus provides a 5-volt reference for more than one sensor. A fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference bus. The ECM monitors the voltage on the 5-volt reference circuits.