108 ENGINE COMPONENT AND LOCATION Inlet Air Heater The optional inlet air heater mounts between the mixer and the inlet manifold. It is activated when the operator turns the key to the preheater position and the engine coolant temperature is lower than 10°C (50°F). Operating time is controlled by the EECU. The operating relay is mounted on the inlet manifold. A lighted icon on the instrument panel signals when the element is On. EGR Diagnostics The EECU commands the EGR valve position and monitors electric current consumed by the EGR valve. An abnormally high reading indicates a jammed EGR valve. The EECU verifies that its command was sent and that the valve position reflects the command.
If the valve is jammed, or its position doesn’t change when commanded, the EECU sets fault codes. A degraded EGR cooler results in low efficiency. The EECU calculates efficiency by comparing EGR gas temperature with engine coolant and exhaust temperatures. An EGR cooler clogged with soot also causes a fault code to be set.