Powertrain, generic (extended)

P2604 Intake Air Heater A Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Worn or sticking intake air heater relay
Loose or burnt terminals on the heater supply cable
Degraded or partly open heater grid
Outdated engine software (manufacturer update available)

Symptoms

  • Hard starting in cold weather
  • White smoke and rough running after a cold start
  • Check engine light

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–600
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

intake air heaterintake air heater relayheater wiring

Related codes

P0540P0541P0542P0543P2605P2609

References: law.cornell.edu, static.nhtsa.gov, static.nhtsa.gov.