P0640 Intake Air Heater Control Circuit

P0640 indicates an intake air heater control circuit problem. The controller cannot command or monitor the heater circuit used to warm incoming air correctly.

Code details

Generic OBD-II · P0

System: Computer
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace cold-start fuel or glow components until the intake air heater control circuit is tested.

Symptoms of P0640

Check-engine light, sometimes with several unrelated codes at once.
Warning lights, a no-start, or intermittent electrical faults.
Communication or module-reset problems on a scan tool.

Common causes of P0640

Low battery voltage, poor grounds, corroded connectors, or blown fuses.
Wiring or network (CAN bus) faults between modules.
A module software/programming issue, or rarely a failed controller.

Useful checks before replacing parts

Check intake air heater command, relay or module output, current draw, battery voltage, intake temperature, coolant temperature, and freeze-frame data.
Inspect heater element resistance, fuse links, relay contacts, high-current wiring, grounds, connector heat damage, and control module driver output.
Command the heater where supported and verify both electrical load and intake temperature response during cold conditions.

Related OBD-II codes

These nearby computer entries can help compare wording and pin down the fault area.