Circuit/System Description
WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The exhaust gas recirculation (EGR) temperature sensors are variable resistors that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the signal circuit and a ground for the low reference circuit. The ECM uses this rationality diagnostic to determine if the input from the EGR temperature sensor 1 or EGR temperature sensor 2 is skewed. The ECM will compare the temperature difference between the EGR temperature sensor 1 and the EGR temperature sensor 2 to determine if the temperatures are within an acceptable operating range of each other.