Intake Air Heater Control Circuit
The engine's intake air heater isn't working properly—think of it like a hair dryer for cold air entering the engine to help it start and run smoothly in winter. When this circuit fails, the ECU can't warm the incoming air as needed.
The ECU monitors voltage and current flow to the intake air heater element, expecting proper resistance and amperage draw when the heater relay activates. It detects an open circuit, short to ground, or excessive resistance that prevents the heating element from reaching operating temperature.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Heater Element Resistance | 4-14 ohms (varies by design) | Out of range or infinite resistance (open circuit) |
| Control Circuit Voltage | 12V applied when active | 0V or voltage not reaching heater element |
Code P0640 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0640 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.