Intake Air Heater A Circuit Range/Performance
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.
Can I keep driving? Fine to drive — worst case is harder, rougher cold starts in very cold weather until repaired.
Real-world scan data
Appears alongside · share of P2604 scans
Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.
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?+
Can I just clear P2604?+
Related codes
Read & clear P2604 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.