Intake Air Heater Control Circuit
P0640 indicates the engine control module detected a malfunction in the intake air heater control circuit, which preheats incoming air on cold starts to improve combustion and driveability. This code sets when the PCM cannot properly control or detect the intake air heater relay or heating element.
What You Might Notice
- Rough idle during cold starts
- Diminished fuel efficiency in cold weather
- Poor engine performance when cold
- Difficulty starting in cold conditions
- Check engine light illumination
Most Common Causes
- 1
Defective intake air heater relay
The relay controlling the heating element fails to switch properly or remains stuck, preventing the heater from activating or deactivating as commanded by the PCM.
- 2
Burnt out intake air heater element
The heating element itself has burned out or failed, unable to generate heat even when power is supplied to it.
- 3
Defective intake air temperature sensor
The IAT sensor provides incorrect readings to the PCM, causing it to think the heater circuit is malfunctioning when it is actually operating correctly.
- 4
Wiring or connector damage
Shorted, open, or corroded wiring and connectors in the heater circuit prevent proper electrical signals between the PCM and heater components.
How to Diagnose It
- 1
Check Defective intake air heater relay — The relay controlling the heating element fails to switch properly or remains stuck, preventing the heater from activating or deactivating as commanded by the PCM.
- 2
Check Burnt out intake air heater element — The heating element itself has burned out or failed, unable to generate heat even when power is supplied to it.
- 3
Check Defective intake air temperature sensor — The IAT sensor provides incorrect readings to the PCM, causing it to think the heater circuit is malfunctioning when it is actually operating correctly.
- 4
Check Wiring or connector damage — Shorted, open, or corroded wiring and connectors in the heater circuit prevent proper electrical signals between the PCM and heater components.
How to Fix It
- 1
Replace intake air heater relay
Locate the relay in the fuse/relay panel under the hood, remove it, and install a new relay of the same specifications. Test for code clearing after installation.
- 2
Replace intake air heater element
Access the heater element in the intake manifold or air intake housing, disconnect electrical connectors, remove the old element, and install a new one with proper torque specifications.
- 3
Repair or replace wiring harness
Inspect all connectors and wiring in the heater circuit for corrosion, damage, or loose connections. Clean corroded connectors or replace damaged wire sections as needed.
- 4
Replace intake air temperature sensor
Remove the IAT sensor from the intake manifold or air intake tube, install a new sensor, and ensure proper electrical connection. Verify sensor readings with a diagnostic scanner.
Need a deeper diagnosis?
Search for related repair guides or browse by system.