P0640
UniversalThe Intake Air Heater Control Circuit code indicates a detected malfunction in the electrical circuit that controls the intake air heater system.
Medium SeverityThis code signifies an electrical problem within the circuit that operates the intake air heater. The intake air heater is crucial for warming the incoming air, especially in diesel engines during cold conditions, to facilitate proper combustion and reduce emissions, meaning a fault can lead to difficult cold starts.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before performing any electrical repairs to prevent accidental short circuits or electric shock. Allow the engine to cool down completely before working on any hot components.
Common Symptoms
- Hard starting in cold weather
- Increased white or black smoke during cold starts
- Poor fuel economy (potentially)
- Check Engine Light illuminated
- Reduced engine performance immediately after a cold start
Common Causes
- Faulty intake air heater element
- Damaged or corroded wiring or connectors in the heater circuit
- Malfunctioning intake air heater relay
- Blown fuse for the intake air heater circuit
- Faulty Engine Control Module (ECM), though rare
Frequently reported on: Ford F-Series (diesel models) 2003-2010, Ram 2500/3500 (Cummins diesel) 2007-2012, Chevrolet Silverado/GMC Sierra (Duramax diesel) 2001-2007
Diagnostic Steps
- Inspect the fuse associated with the intake air heater in your vehicle's fuse box and replace if blown.
- Visually check all wiring and connectors leading to the intake air heater for signs of damage, corrosion, or looseness.
- Test the intake air heater relay for proper operation using a multimeter or by swapping it with a known good relay (if applicable and identical).
- If accessible, test the resistance of the intake air heater element itself using a multimeter to check for an open circuit or short.
- Ensure proper voltage supply to the heater circuit when the heater should be active (e.g., during cold start conditions).
👨🔧 When to Call a Professional
If you lack experience with electrical diagnosis using a multimeter or cannot locate the specific fault after basic checks, it is best to consult a professional mechanic. Complex wiring issues or PCM-related problems often require specialized diagnostic tools.
Commonly Asked Questions
What does the intake air heater do?
It warms the air entering the engine, especially crucial for diesel engines in cold weather to aid combustion and reduce emissions.
Can I drive with a P0640 code?
While you might be able to drive, you may experience hard starting, increased smoke, and reduced performance in cold conditions. It's best to address it to prevent potential engine strain or incomplete combustion issues.
Is the intake air heater the same as glow plugs?
No, glow plugs heat the combustion chamber directly, primarily in diesel engines, while the intake air heater warms the air BEFORE it enters the engine. Some engines use one or both systems.
How can I test the intake air heater relay?
You can test the relay by checking for continuity across the switch terminals when the coil is energized, or by swapping it with an identical, known-good relay to see if the symptom changes.
What tools do I need for this repair?
Basic hand tools, a multimeter for electrical diagnostics, and potentially a wiring diagram for your specific vehicle.