A vehicle with a DTC for an engine coolant temperature out of range code is being tested. The serial data stream shows the coolant temperature to be 198 degrees Fahrenheit. When the technician tests the resistance between the ETC terminals, he finds infinite resistance. The specifications call for 20 to 40 ohms at 200 degrees Fahrenheit. After the ECT is replaced and the code is erased, the system runs normally and the code and MIL illumination do not reoccur. How is this possible?
A)There was excessive air in the cooling system; when the ECT sensor was removed, the trapped air bled out
B)The ETC code was set by a loose connection where the harness meets the ECT terminals; disconnecting and reconnecting the plug essentially fixed the problem
C)The problem is an intermittent electrical fault; it will eventually reoccur
D)When the ECT failed, the PCM substituted a nominal ECT value that allowed the engine to run in limp home mode; the substituted value was displayed by the scan tool

Question

Quizplus · Accepted Answer

The PCM substituted a nominal value for the engine coolant temperature (ECT) when the sensor failed, which is why the scan tool displayed a temperature of 198 degrees Fahrenheit despite the sensor having infinite resistance, indicating it was faulty. This substitution allowed the engine to continue operating in a "limp home" mode until the issue was resolved.

A Vehicle with a DTC for an Engine Coolant Temperature