Intake Air Heater Control Circuit Malfunction
The P0640 code indicates a malfunction in the intake air heater control circuit. This heater is used in diesel engines to warm the intake air for improved cold-start performance. The Powertrain Control Module (PCM) monitors the circuit for proper voltage and current. When the circuit is open, shorted, or has excessive resistance, the PCM sets this code. Common causes include a faulty heater relay, damaged wiring, a blown fuse, or a defective intake air heater element.
1. Most Common Causes
- Faulty or burned-out intake air heater (IAH)
- Open circuit, short to ground, or short to voltage in the wiring
- Corroded, loose, or damaged connector or terminal
- Defective intake air heater control relay
- Internal ECM/PCM failure in the circuit driver
- Blown intake air heater circuit fuse
2. Symptoms You Will Notice
- Hard starting in cold weather
- Check Engine Light illuminated
- Excessive white smoke on startup
- Rough idle until engine warms up
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0640 and check for related codes.
Step 2: Inspect the intake air heater fuse and relay; replace if blown or faulty.
Step 3: Visually inspect wiring and connectors for damage, corrosion, or loose connections.
Step 4: Test the heater element resistance with a multimeter; compare to manufacturer specs.
Step 5: Check for power and ground at the heater connector with the key on; repair as needed.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe to drive, but you may experience hard starting in cold weather and increased emissions. It's best to repair it promptly to avoid potential starting issues.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on the specific cause and vehicle model.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.