JLG 450A_AJ Series II Service Manual - Manual (Page 160)

SECTION 3 - CHASSIS & TURNTABLE
3-120 – JLG Lift – 3121290
DTC 118- ECT/CHT High Voltage
• Engine Coolant Temperature Sensor
• Check Condition-Engine Running
• Fault Condition-CHT/ECT sensor voltage higher than the
limit defined in the diagnostic calibration
• Corrective Action(s)- Sound audible warning or illuminate
secondary warning lamp, disable adaptive learn fueling
correction during active fault, or any combination thereof
as defined in calibration. Recommend a power derate 1/2
to reduce the possibility of engine damage due to the
inability to sense temperature.
• Non-emissions related fault
The Engine Coolant Temperature sensor is a thermistor (tem-
perature sensitive resistor) located in the engine coolant.
Some engines use an ECT sensor that is located in the coolant
near the thermostat. Some engines use a CHT (Cylinder Head
Temperature) sensor that is located in the coolant in the cylin-
der head. If the engine is equipped with an ECT sensor then
the CHT value is estimated. If equipped with a CHT sensor then
the ECT value is estimated. The ECM provides a voltage divider
circuit so that when the coolant is cool, the signal reads higher
voltage, and lower when warm.
This fault sets if signal voltage is higher than high voltage limit
as defined in diagnostic calibration anytime engine is running.
The limit is generally set to 4.90 VDC. In many cases, this condi-
tion is caused by the CHT/ECT sensor being disconnected from
the engine harness, an open-circuit or short-to-power of the
CHT/ECT circuit in the wire harness, or a failure of the sensor.
The ECM will use a default value for the CHT/ECT sensor in the
event of this fault.