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152
TM 9-2320-312-24-2
Troubleshooting Section
The air inlet heater will turn on if the coolant
The air inlet heater and the lamp for the air inlet
temperature sensor has an active open circuit
heater should turn on. The air inlet heater and the
diagnostic code or an active short circuit diagnostic
lamp for the air inlet heater should turn off when the
code and the inlet manifold air temperature is less
cycle is complete.
than 10 C (50 F).
The ECM will control the air inlet heater for the
"Cranking Cycle" if the operator starts the engine
The air inlet heater will turn on if the air temperature
before the end of the heating cycle.
sensor for the inlet manifold has an active open
circuit diagnostic code or an active short circuit
diagnostic code and the coolant temperature is less
Control of the Air Inlet Heater During Engine
than 40 C (104 F).
Cranking
If the sum of the coolant temperature and the inlet
Note: The coolant temperature and the inlet manifold
manifold air temperature is less than 25 degrees
temperature are measured in degree Celsius. An
Celsius or 109 degrees Fahrenheit, the air inlet
electronic service tool can display the coolant
heater will turn on when the engine is cranking. The
temperature and the inlet manifold temperature in
heater will remain on while the engine is cranking.
degree Celsius or in degree Fahrenheit. The ECM
The air inlet heater will reactivate for 30 seconds if
adds the coolant temperature and the inlet manifold
the engine fails to start.
temperature together. Then, the ECM uses the
sum of the coolant temperature and the air inlet
temperature in order to determine if the air inlet
Engine Start Cycle
heater should be on or off. Illustration 31 is a visual
The operation of the air inlet heater is determined
aid for troubleshooting the operation of the air inlet
by the coolant temperature and the inlet manifold
heater. The temperatures in degree Fahrenheit
air temperature after the engine has started. If the
are not a direct conversion of the temperatures in
combined temperature is less than 25 degrees
degree Celsius.
Celsius or 109 degrees Fahrenheit, the engine
start cycle begins. The engine start cycle has two
The following procedure explains the temperatures
segments:
that are shown in degree Fahrenheit:
Continuous Mode
Convert the reading for the coolant temperature
from degree Celsius to degree Fahrenheit.
On/Off Cycling Mode
Convert the reading for the inlet manifold
The Continuous Mode lasts for a maximum of seven
temperature from degree Celsius to degree
minutes. The On/Off Cycling Mode can last for a
Fahrenheit.
maximum of thirteen minutes. The air inlet heater
Add the two conversions together in order to
is turned on and the air inlet heater is turned off
for ten seconds during the On/Off Cycling Mode.
arrive at the correct conversion for the sum in
The air inlet heater will turn off when the sum of
degree Fahrenheit.
the coolant temperature and the inlet manifold air
temperature exceeds 35 degrees Celsius or 127
degrees Fahrenheit.
Note: MAY99 and newer Personality Modules
use the boost pressure reading to determine
atmospheric pressure. This will indicate if the
engine is operating above 1678 m (5505 ft). If the
altitude is above 1678 m (5505 ft), the temperature
calculation is adjusted in order to compensate for
the extreme altitude. The temperature calculation is
used in order to determine the operation of the air
inlet heater. Refer to Illustration 31 for more details.
Active Open Circuit or Short Circuit Diagnostic
Codes

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