ECM DETERMINES by cylinder(s) and exhaust manifold temp sensors.

https://www.manualslib.com/download/1241779/Suzuki-Df150.html

OVERHEAT CAUTION
CONDITION 1 (Maximum temperature)
Immediate activation of system when:
• Cylinder temperature reaches 120 °C (248 °F)
• Exhaust manifold temperature reaches 114 °C (237.2 °F)
CONDITION 2 (Temp. rise vs Time)
Immediate activation of system when:
• The average temperature difference during three consecutive 10 second measurement periods of the cyl-
inder temperature sensor at engine speeds of 500 r/min or higher exceeds the limits as shown below.
• The average temperature difference during three consecutive 10 second measurement periods of the
exhaust manifold temperature sensor at engine speeds of 500 r/min or higher exceeds the limits as
shown below.
ACTION:
RESET:
Close throttle completely and then shift into neutral.
System reset will occur when cylinder temperature drops below the limits shown below. However, the sys-
tem may be activated again unless the cause for overheat (such as insufficient water) is removed.
Temperature range Temperature difference

Seem the temp light end is bad.