P2604
Intake Air Heater A Circuit Range/Performance
Intake air heater
Generic OBD-II
Low
What it means
P2604 means the intake air heater circuit isn't performing as the ECM expects. This heater warms incoming air to help cold starts and cut cold-start emissions, common on diesels. The fault is usually a bad heater element, relay, or wiring — the engine still runs fine, though cold starts may be harder or smokier in freezing weather.
Low
Can I keep driving? Fine to drive — worst case is harder, rougher cold starts in very cold weather until repaired.
Common symptoms
What you'll notice
- Check-engine light on with the code stored
- Harder cold starting in cold weather
- Rough running or extra smoke right after a cold start
- Often no noticeable symptom in warm weather
Common causes
Most likely first
- Faulty intake air heater element (grid/PTC heater)Likely
- Open or high-resistance wiring to the heaterCommon
- Faulty heater relay or control driverCommon
- Poor connection or corroded ground at the heaterLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data to see the conditions when it set.
- Inspect the heater element, its connector, and ground for corrosion or damage.
- Test the heater relay and measure the heater's current draw or resistance.
- Check the control wiring for opens or high resistance.
- Replace the heater element if it is open or out of spec. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P2604?+
Yes. The intake air heater only aids cold starts and emissions. You may notice harder cold starts in freezing weather, but the engine runs normally otherwise.
Can I just clear P2604?+
It will come back once the ECM runs the heater test again. The heater circuit needs repair to clear it for good.
Related codes
Often seen with P2604
Read & clear P2604 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