Control of the Air Inlet Heater During Engine Cranking

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