P2604

Code

Generic P — Powertrain

Intake Air Heater A Circuit Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 27 EN: 40 RU: 28

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Page language: EN

Causes

Open or shorted wiring in the intake air heater A circuit
Loose, corroded, or damaged connector at the heater or control module
Blown fuse or faulty relay supplying the heater circuit
Failed intake air heater element (open or partially shorted)
High resistance in ground or supply (corrosion, damage, poor connection)
Faulty PCM/ECM driver or internal control circuitry

Symptoms

MIL (Check Engine) lamp illuminated
Difficult cold starts or extended cranking in cold conditions
Increased white smoke or rough idle during cold start
Reduced engine performance or poor emissions until engine warms
Stored fault code(s) related to intake air heater circuit

What to check

Scan tool: read freeze frame, pending/active status and other stored codes
Inspect fuses and relays related to intake air heater circuit
Visual inspection of wiring harness, connectors and heater module for damage, corrosion, or water intrusion
Measure supply voltage at heater connector with heater commanded ON
Measure resistance of heater element (with circuit disconnected) and compare to specification
Check ground integrity and continuity from heater to chassis/engine

Signal parameters

Supply voltage at heater connector: approx. near battery voltage when commanded ON (exact spec varies by vehicle)
Heater element resistance: low ohms (typically a few ohms — consult vehicle service data for exact value)
Current draw when heater is commanded: moderate to high (amperes) — compare to service spec
PCM command signal: switched battery voltage or PWM duty cycle depending on design
Expected change in circuit current/resistance when heater is commanded ON vs OFF

Diagnostic algorithm

Retrieve codes and freeze frame with a scan tool. Note engine temperature and conditions when code set.
Perform visual inspection of intake air heater, wiring, connectors, fuses and relay. Repair obvious damage or corrosion.
With ignition OFF, disconnect the heater connector and measure heater element resistance to ground and between terminals. Compare to manufacturer spec. Replace heater if open or out of spec.
Check fuse(s) and relay(s) in the heater supply circuit. Replace any blown fuses or suspect relays. Verify relay control and supply continuity.
With scan tool, command the intake air heater ON (if supported). Measure supply voltage at the heater connector. Voltage should be present when commanded; if not, trace supply back to fuse/relay/PCM.
While commanded ON, measure current draw using a clamp meter in the supply feed. Compare to spec. Very low or no current indicates open circuit; excessive current indicates short or partially shorted element.
Check continuity and resistance of harness from heater connector to PCM and to ground. Repair any high resistance or intermittent circuits (replace wiring or connectors as required).
If wiring and heater element test good, test PCM output driver using scope or suitable diagnostic method per service manual. Replace PCM only after confirming driver fault and after ruling out harness and heater.
After repairs, clear codes, perform key cycles and run conditions to ensure code does not return. Re-check for proper heater operation during cold start conditions.

Likely causes

Corroded connector at the intake air heater or battery/fuse
Heater element degraded or partially shorted causing abnormal current
Blown fuse or weak/failed relay in heater supply circuit
Open circuit in heater wiring due to chafing or broken conductor
PCM output transistor failed or intermittent

Fault status

⚠️ Status

Intake Air Heater A circuit out of expected range or performance. Indicates abnormal electrical behavior (voltage, current, or resistance) when heater is commanded. Requires inspection of heater element, wiring, connectors, fuses/relays and PCM driver.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours