P0640 — Intake Air Heater Control Circuit #

Note: The exact wording of this code’s title may vary by manufacturer (OEM).

• “Intake Air Heater ‘A’ Control Circuit” (Chrysler, Dodge, Jeep, RAM)
• “Intake Air Heater Control Circuit Malfunction” (Ford, General Motors, Chevrolet)
• “Intake Air Preheater Circuit Fault” (Nissan, Toyota)

Code Summary for P0640 #

The P0640 diagnostic trouble code (DTC) indicates a problem detected in the intake air heater control circuit. The intake air heater, sometimes called a grid heater, is an electrical component designed to warm incoming air in the intake manifold, primarily found on diesel engines. This assists with cold-weather starting and reduces emissions by improving combustion. When the engine control module (ECM) or powertrain control module (PCM) detects abnormal voltage or resistance in the heater circuit, it sets code P0640 and often activates the check engine light. Immediate attention is recommended to avoid hard starting and increased exhaust emissions.

Common Symptoms for Code P0640 #

A vehicle with a stored P0640 code often displays noticeable changes in engine performance, especially in cold weather. Recognizing these signs can help you diagnose the problem faster and prevent further issues.

• Hard starting in cold weather
• Rough idle during cold starts
• Longer cranking time before engine fires up
• Check Engine Light (CEL) illuminated
• Occasionally, increased exhaust smoke at startup

Probable Causes for Code P0640 (in order of frequency) #

Several factors can trigger a P0640 code, and some are more common than others. Understanding the most likely culprits ensures a quicker, more efficient repair process.

1. Failed intake air heater element (burned out or open circuit)
2. Faulty intake air heater relay or control module
3. Damaged wiring (open, shorted, or corroded wires/connectors in the heater circuit)
4. Blown fuse in the heater circuit
5. ECM/PCM malfunction (rare)

Step-by-Step Diagnosis for Code P0640 #

Diagnosing P0640 is like being a detective—methodically checking each link in the circuit until you find the culprit. Here’s how to proceed:

• Step 1: Confirm the code with a scan tool and note any other related codes.
• Step 2: Perform a visual inspection of the intake air heater, relay, fuse, and connectors for obvious damage, corrosion, or loose connections.
• Step 3: Check the fuse related to the intake air heater circuit and replace if blown.
• Step 4: Use a multimeter to test for proper voltage at the heater element and relay; verify ground connections.
• Step 5: Test the intake air heater element for continuity (an open circuit indicates a failed heater).
• Step 6: If all external components test good, check for control signals from the ECM/PCM to the relay and heater.
• Step 7: Clear the code and retest after repairs; verify the heater operates during a cold start.

Possible Repairs for Code P0640 #

Repairing a P0640 code depends on which component is at fault. Address the most common failures first to restore smooth, reliable starting.

• Replace a failed intake air heater element
• Replace a faulty relay or intake air heater control module
• Repair or replace damaged wiring or connectors in the circuit
• Replace a blown fuse and investigate the cause
• In rare cases, reprogram or replace the ECM/PCM after confirming all other causes

Can You Drive with Code P0640? #

Limited: While most vehicles will still run with a P0640 code, driving with this issue—especially in cold climates—can lead to hard starting, increased smoke, and rough idle. There’s no immediate risk of catastrophic engine damage, but persistent driving may stress the starter, battery, and increase emissions. Prompt repair is strongly encouraged for reliable operation and environmental compliance.

Vehicles Most Commonly Affected by Code P0640 #

P0640 is most often found in modern diesel vehicles, particularly those from manufacturers who use intake air heaters as standard cold-start equipment. While it can technically affect any vehicle with an intake air heater, the following brands and models appear more frequently in repair shops with this code:

• RAM (2500, 3500, 4500, 5500 series with Cummins Diesel)
• Dodge (Diesel trucks and vans)
• Chevrolet Silverado/GMC Sierra (Duramax Diesel)
• Ford Super Duty (F-250, F-350 with PowerStroke Diesel)
• Nissan Titan XD (Diesel models)
• Jeep Grand Cherokee (Diesel models)
• Some Toyota Land Cruiser/HiLux with diesel engines

Common Mistakes & Best Practices for P0640 #

It’s easy to misdiagnose P0640 if you rush or overlook key steps. Professional technicians recommend slowing down and verifying each component before replacing expensive parts.

• Don’t replace the intake air heater element before testing the relay, fuse, and wiring.
• Always check for related codes (such as glow plug or relay faults) for a more complete picture.
• Carefully inspect connectors for corrosion or pushed-out pins.
• Never ignore a blown fuse: replacing it without finding the cause may result in repeated failures.
• After any repair, clear the code and confirm a cold start test to verify success.

Express FAQ — P0640 #

Still have questions? Here are quick answers to help you understand and solve code P0640.

• Q: Can a bad intake air heater cause hard starting even if the weather is mild?
  A: Typically, the heater is most critical in cold weather. In mild temperatures, you may notice little or no starting issues, though the code and check engine light will still be present.
• Q: Will fixing P0640 improve fuel economy or performance?
  A: While direct fuel economy gains are minor, fixing the code ensures smoother starts, less smoke, and helps protect other components, like the starter and battery.