P2604 code meaning
Intake Air Heater A Circuit Range/Performance
Powertrain system Generic code P26xx codes Check engine light
What P2604 means
P2604 is the functional check of intake air heater A - the grid heater in the intake that warms the charge air of a diesel engine for cold starts. The circuit responds, but current, voltage drop or heating effect do not match the command. Under CARB, a glow plug or intake air heater has to be checked both for reacting correctly when commanded and for plausible current and voltage drop in its circuit. Volvo's heavy-truck engine bulletins (2020, 2022) list P2604-7F among the codes caused by a weak pre-heat relay and fix it with a software update, a check of terminal tension at heater and relay, and a new relay plus supply cable. P0540-P0543 cover the electrical faults of heater A, P2605-P2608 heater B, P2609 the system. Expect hard cold starts and white smoke.
P2604 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P2604
- Hard starting in cold weather
- White smoke and rough running after a cold start
- Check engine light
Common causes of P2604
- Most likelyWorn or sticking intake air heater relay
- PossibleLoose or burnt terminals on the heater supply cable
- PossibleDegraded or partly open heater grid
- Less likelyOutdated engine software (manufacturer update available)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Intake air heaterIntake air heater relayHeater wiring
What each part of P2604 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 6 | Area: computer (engine control module) and output circuits. |
| 04 | The exact fault in that area. |
What to do next
- Note P2604 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P2604
What does P2604 mean?
P2604 means "Intake Air Heater A Circuit Range/Performance". P2604 is the functional check of intake air heater A - the grid heater in the intake that warms the charge air of a diesel engine for cold starts. It is a generic code, so it means the same on every make.
Is it safe to drive with P2604?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P2604 fail an emissions test?
Yes, it can. P2604 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P2604 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P2604 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.