P0640
Intake Air Heater Control Circuit
Intake air heater
Generic OBD-II
High
What it means
P0640 means the ECM detected a fault in the intake air heater control circuit. This heater warms incoming air to aid cold starts, so a fault mainly shows up as hard starting and rough warm-up in cold weather. It is usually a relay, fuse, wiring, or heater-element problem.
High
Can I keep driving? Usually driveable in mild weather, but expect hard cold starts and rough warm-up until the intake air heater circuit is fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Hard starting in cold weather
- Rough idle or stalling during warm-up
- Reduced performance and economy on cold starts
Common causes
Most likely first
- Faulty intake air heater relayLikely
- Blown fuse in the intake air heater circuitCommon
- Wiring or connector fault in the heater control circuitCommon
- Faulty intake air heater control moduleLess often
- Defective intake air heater elementLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check the intake air heater fuse and relay first.
- Inspect the heater control wiring and connectors for damage, looseness, or corrosion.
- Test the intake air heater relay and replace it if it fails.
- Measure the heater element's resistance and replace it if open or out of spec.
- Test/replace the heater control module if the circuit checks out, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0640?+
In mild weather, generally yes. In cold weather the engine may be hard to start and run rough while warming up. Fix it before winter conditions.
Can I just clear P0640?+
It will return until the relay, fuse, wiring, or heater element is repaired. Clearing it won't restore cold-start heating.
Related codes
Often seen with P0640
Read & clear P0640 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX