P2608

Code

Generic P — Powertrain

Intake Air Heater B Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 29 EN: 42 RU: 23

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Page language: EN

Causes

Short to battery voltage on Intake Air Heater B control circuit
Faulty/intentionally stuck closed relay or fuse feeding the heater
Damaged, corroded, or loose connector or wiring (insulation chafing, pin corrosion)
Failed intake air heater element (internal short or open)
Poor ground or high-resistance connection in the heater circuit
Faulty ECM/input driver

Symptoms

Malfunction Indicator Lamp (MIL) illuminated / DTC stored
Difficulty or extended cranking on cold starts
Rough idle or increased smoke during cold start
Reduced cold-start performance or longer warm-up
Possible no-start in extreme cases (if heater required for starting)

What to check

Read and record stored codes and freeze frame data; clear codes and re-run test
Visual inspection of intake air heater harness, connectors, and relay/fuse for damage, corrosion, heat discoloration
Check relevant fuses and relays for stuck/shorted condition
Measure battery voltage to ensure proper supply (11–15 V range)
Back-probe ECM connector to measure voltage on Intake Air Heater B circuit with heater commanded and not commanded
Measure resistance of the intake air heater element(s) per vehicle specification

Signal parameters

Battery nominal voltage: ~12–14.5 V (engine running ~13.5–14.5 V)
ECM control line expected low when activated: typically
Circuit high condition typically flagged when measured voltage at ECM input is well above expected control voltage (often >5–7 V depending on manufacturer threshold)
Intake air heater element typical cold resistance: varies by design (commonly a few ohms to a few tens of ohms) — consult vehicle specs
Expect open-circuit (infinite) resistance only if heater is physically disconnected; a short to battery will show full battery voltage on the control pin with heater disconnected

Diagnostic algorithm

Retrieve freeze frame and related codes. Confirm P2608 is current and note conditions (ambient temp, engine run state).
Perform a visual inspection of the intake air heater assembly, connectors, and harness for damage, melted insulation, corrosion, or rodent damage.
With ignition off, disconnect the intake air heater connector and measure heater element resistance to its specification. Replace heater if resistance is out of range (open circuit or shorted).
Inspect and test fuse(s) and relay(s) in the heater supply circuit. Remove relay and see if voltage on the heater control/ECM pin changes.
With connector disconnected, measure voltage at the harness power feed and at the ECM control pin. Check for short-to-battery (unexpected battery voltage present at control pin when circuit should be off).
Back-probe ECM input for Intake Air Heater B and observe voltage while commanding the heater (using scan tool) and while not commanded. Compare to expected behavior (
Check continuity from ECM connector to heater connector for shorts to power and ground and for open circuits. Repair any damaged wiring or poor pin contact.
If wiring, connectors, heater element, relays/fuses are good but fault persists, consult vehicle wiring diagrams and consider ECM input/driver fault—verify with manufacturer procedures before replacing ECM.
After repairs, clear codes and perform verification cold-start tests to confirm correct heater operation and that P2608 does not return.

Likely causes

Shorted circuit to battery (power feed) at harness or connector
Corroded/mis-seated connector at heater or ECM
Defective heater element with abnormal internal path
Stuck relay supplying constant power to heater
High resistance/poor ground causing abnormal voltage reading
Intermittent ECM input failure (less common)

Fault status

⚠️ Status

Stored when the ECM detects voltage on the Intake Air Heater B control circuit above the allowable threshold. MIL may be illuminated. Code can be intermittent depending on wiring or connector condition.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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