Illustration 28 Location Of Components

TM 9-2320-312-24-2

Systems Operation Section

Running of the engine

After the engine has started, the same combination

of inlet manifold air temperature and coolant

temperature will determine the state of the heater.

The cycle has two strategies.

The two strategies are continuous and intermittent.

During the continuous strategy, the heater will

remain on for a maximum of 7 minutes after starting.

If the same conditions exist, the ECM will activate

the intermittent strategy. During the intermittent

strategy, the heater is cycled for a maximum of 13

minutes. During this cycle, the heater is turned on

for 10 seconds and the heater is turned off for 10

seconds. After the 13 minute time limit, the heater

is shut off.

When one of the temperature sensors fails, the

system will operate in the following manner:

Coolant temperature sensor

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Illustration 28

Location Of Components

When the coolant temperature sensor has an open

(1) Relay of the air inlet heater. (2) Inlet air temperature sensor. (3)

circuit or a short circuit, the coolant temperature

Ground strap (heater to engine). (4) Air inlet heater. (5) Coolant

sensor has failed. During this condition, the

temperature sensor. (6) ECM.

heater will be activated when the inlet manifold air

temperature is less than 10 C (50 F).

The relay for the air inlet heater (1) is located on the

mounting bracket for the fuel filter. The relay turns

Inlet air temperature sensor

the 12 V heater ON and OFF in response to signals

from the ECM (6).

When the inlet air temperature sensor has an open

circuit or a short circuit, the inlet air temperature

The air inlet heater (4) is a component of the air

sensor has failed. During this condition, the heater

inlet cover. The heater element has a ground strap

will be activated when the coolant temperature is

(3) that must be connected to the engine.

less than 40 C (104 F).

There are three conditions that would cause the air

Under the proper condition, the heater will

inlet heater to be activated:

be reactivated. When the sum of the coolant

temperature and the inlet manifold air temperature

Powerup and Mode of Preheat

has dropped below 25 C (109 F), the heater will

be reactivated. This condition could exist after a

Regardless of temperature, the heater and the lamp

warm engine has cooled and the operator attempts

of the heater should come on for two seconds

to start the engine.

when the ECM is first powered (lamp check). When

the sum of the coolant temperature plus the inlet

When the sum of the coolant temperature and the

manifold air temperature is less than 25 C (109 F),

inlet manifold air temperature does not attain 35 C

the ECM will turn on the heater and the lamp for 30

(127 F), the heater will be activated. The heater can

seconds. This is a cycle of preheat.

be activated no longer than 20 minutes (maximum).

The ECM will turn off the heater after the 20 minute

The ECM will then turn off the heater and the lamp.

time limit.

When the operator attempts to start the engine prior

to the completion of preheat, the ECM proceeds

For additional information on the air inlet heater,

into the mode of cranking for heater control.

refer to Troubleshooting, "Air Inlet Heater Circuit -

Test".

Mode of cranking

During engine cranking, when the sum of the

coolant temperature plus the inlet manifold air

temperature is less than 25 C (109 F), the ECM will

turn on the heater. The heater will remain on during

engine cranking. If the engine fails to start, the ECM

reverts to preheat. Reverting to preheat will activate

the heater for another 30 seconds.