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Why does the engine fan run continuously on a Detroit diesel 12.7 liter when temperature and ac high low pressure are o.k.?

There are a few possible reasons why the engine fan on a Detroit diesel 12.7 liter might be running continuously, even when the temperature and AC high low pressure are okay.

* The engine coolant temperature sensor may be faulty. This sensor is responsible for sending a signal to the engine control module (ECM) indicating the temperature of the engine coolant. If the sensor is faulty, it may be sending an incorrect signal to the ECM, causing the fan to run continuously.

* The ECM may be faulty. The ECM is responsible for controlling the operation of the engine fan. If the ECM is faulty, it may be sending an incorrect signal to the fan, causing it to run continuously.

* There may be a problem with the wiring or connections to the engine fan. If the wiring or connections to the fan are damaged or loose, the fan may not be receiving the correct electrical signal, causing it to run continuously.

If you are not able to identify and fix the problem yourself, you should take your vehicle to a qualified mechanic for diagnosis and repair.