The function diagram for the ECT sensor includes the following:
• ECT sensor
• Electronic Control Module (ECM)
• Exhaust Gas Recirculation (EGR)
• Injector Drive Module (IDM)
• Fuel injector
• Variable Geometry Turbocharger (VGT)
• ENGINE lamp (amber and red)
The ECT sensor is a thermistor sensor installed in the water supply housing (Freon® compressor bracket),
right of the flat idler pulley assembly. The ECM supplies a 5 V reference signal which the ECT sensor uses to produce an analog voltage that indicates temperature.
The ECT sensor changes resistance when exposed to different temperatures. As the coolant temperature decreases, the resistance of the thermistor increases.
This causes the signal voltage to increase. As the coolant temperature increases, the resistance of the thermistor decreases. This causes the signal voltage to decrease.
The ECT sensor provides a feedback signal to the ECM indicating engine coolant temperature. The ECM monitors the ECT signal to control the following features:
• Engine Warning and Protection System (EWPS)
• Cold Ambient Protection (CAP)
• Idle Shutdown Timer (IST)
• Cold idle advance
• Coolant compensation
During engine operation, if the ECM recognizes that the ECT signal is greater or less than the expected value it will set a Diagnostic Trouble Code (DTC).
Coolant Temperature Compensation
Coolant temperature compensation reduces fuel delivery if ECT is above cooling system specification.
The reduction in fuel delivery begins when ECT reaches approximately 107 °C (225 °F). A relatively rapid reduction of 15% will be achieved as the ECT reaches approximately 110 °C (230 °F).
Fuel reduction is calibrated to a maximum of 30% before standard engine warning or optional warning/protection is engaged. If warning or shutdown occurs, a DTC is stored in the ECM memory.
NOTE: Coolant temperature compensation may be disabled in emergency vehicles that require 100%
power on demand.
Engine Warning and Protection (EWPS)
The EWPS is an optional feature that can be enabled or disabled. When enabled, the EWPS will warn the operator of an overheat condition and can be programmed to shut down the engine.
The red ENGINE lamp will come on when ECT reaches approximately 109 °C (228 °F). A warning buzzer will sound when ECT reaches approximately 112 °C (234 °F). The engine will shut down when the ECT reaches approximately 112 °C (234 °F), if 3-way protection is enabled.