Possible causes

– Faulty Intake Air Heater
– Intake Air Heater harness is open or shorted
– Intake Air Heater circuit poor electrical connection

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0640 Description

The intake air (IA) heater 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 IA heater ON when the engine coolant temperature is below 40 C (104 F). The power to the IA heater is supplied by the battery positive voltage circuit.

P0640 Information for specific makes

P0640 FORD
P0640 GMC