The intake air heater (IAH) is located in the air inlet tube and is used to warm the incoming air to aid in starting the engine and for proper cylinder combustion. The glow plug control module (GPCM) will command the IAH on when the engine coolant temperature is below 40°C (104°F).

The IAH is commanded ON by the GPCM through the command 1 circuit and the command 2 circuits. The command 1 signal is ON or OFF from the GPCM to the IAH. The command 2 circuits are digital signal from the GPCM to the IAH. Without both signals the IAH will not operate. The feedback signal is digital and informs the GPCM of the status of IAH. The temperature, current, and voltage circuits are analog signals from the IAH to the GPCM.

The IAH will be commanded to 100 percent when the engine coolant temperature is below 5°C (41°F) for 180 seconds after key up, then it will ramp down to 42 percent after 180-300 seconds and will hold it there until 300-500 seconds. After 500-600 seconds the IAH will ramp down to 0 percent. When the engine coolant is 10-40°C (50-104°F) the IAH is 100 percent for 30 seconds after key up then ramps down to 42 percent after 30-90 seconds and holds it there for up to 500 seconds, then it ramps down to 0 percent from 500-600 seconds.