Proheat X45–School Bus - Manual (Page 78)

5-21 SECTION 5. TROUBLESHOOTING & REPAIR
A TEMP SENSOR diagnostic code indicates a short or open circuit in the
temperature sensor wiring or the coolant temperature is out of range—below
-58˚F (-50˚C) or above 266˚F (130˚C). The resistance of the temperature
sensor is proportional to temperature.
Check: Temperature Sensor (CODE indicated)
a) Inspect wiring for short or open circuits.
b) Check resistance of sensor. Is it within range as shown in
Figure 5-20. If it is within valid range and the PCM still
displays code on start up, replace PCM.
C) Test the sensor. (See test procedure below.)
Test Procedure:
a) Connect a multimeter (adjusted to measure resistance) to the
temperature sensor as per Figure 5-19. The polarity of the
sensor connections to the multimeter is not important.
b) Measure the sensor resistance versus temperature under
the following conditions:
• at room temperature
• in a freezer
• in boiling water.
c) Compare the measured values against the graph (Figure 5-20).
If values do not approximately match, then the sensor is
defective and must be replaced.
Figure 5-19 Temperature Sensor Test
7 Temp
Sensor