Drawing courtesy VW / Audi Group Figure 7: The "large coolant circuit" is the Audi / VW term for an open thermostat. Traditionally only opened to allow coolant to flow in and out of the radiator when the engine reached the stat's spec (around 195 deg. F) the electric mapped thermostat can open very quickly following an input from the driver's foot on the accelerator. coolant to be pumped through the radiator as the "large coolant flow circuit." (Fig. 7 & 8) The electric mapped thermostat contains a large valve disc and small valve disc as part of the assembly along with a lifting pin. (Fig. 9) (100 KPH) is no longer required on some mapped thermostat models due to the more flexible control of the engine temperature along with the ram air effect of air over the radiator on a moving vehicle. You may see some other changes related to the cooling system in an electric thermostat equipped vehicle. There are often two ECT sensors on models using electric mapped thermostats. One of the ECTs may be found on or near the coolant manifold (a.k.a. coolant distributor) with the other on the radiator outlet. The ECM uses the engine mounted ECT for actual coolant temperature. With two ECTs, the ECM now uses the temperature difference between the ECT mounted at the engine outlet and the ECT mounted at the radiator outlet to determine the correct operation of the cooling fans. The familiar activation of the electric cooling fan above 60 MPH As with anything electrical that is controlled by a computer you'll want to first establish the customer 's complaint is valid and present and then make basic observations (any obvious disconnections or blown fuses) followed by retrieval of DTCs (in ANY system) before proceeding (Fig. 10). Should you retrieve a P0597-P0599 code there are some very quick checks that require critical thinking that you can perform to check out the circuit. These simple checks would apply to ANY DTC that is reporting a circuit problem to a computer controlled 2-wire actuator ranging from a fuel injector to a compressor clutch. Looking at a simple schematic for a August 2016 Diagnostics 4 MACS Service Reports