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P2607Intake Air Heater "B" Circuit/Open

The control module has detected an open circuit in the intake air heater "B" circuit, the second heater element or relay used to warm intake air for cold starting.

Definition

Engines with dual intake air heater elements (common on diesels with two-stage grid heaters) use separate relays so the ECM can stage heating current. P2607 sets when heater circuit "B" is commanded on but the module sees an open circuit or no current flow. Symptoms concentrate in cold weather: longer cranking, white smoke, and rough running until warm, plus an illuminated MIL that can cause an emissions-test failure; warm-climate driveability is often unaffected.

Common causes

  • Corroded or loose high-current connections at the heater element or relay studs
  • Failed intake air heater "B" relay/solenoid
  • Open heater element
  • Blown fusible link or damaged feed cable for the second circuit
  • Open control or sense wiring to the ECM
  • Failed ECM driver (rare)

Common misdiagnoses

  • Glow plugs on grid-heater-equipped engines
  • Batteries or charging system blamed for slow cold starts
  • Injectors replaced for cold-start smoke
  • Replacing both heater relays when only the circuit B feed cable was broken

Troubleshooting steps

  1. 1.Identify the circuit B relay and feed

    On two-stage systems, confirm from the wiring diagram which relay and cable serve heater "B" so you test the correct leg.

  2. 2.Inspect high-current connections

    Check the element studs, relay terminals, and cable ends for corrosion, heat damage, or looseness, and clean/retorque as needed.

  3. 3.Verify power supply to the relay

    Confirm battery voltage at the relay input; check the fusible link or mega-fuse if it is missing.

  4. 4.Command heater B and measure output

    Use a scan tool to activate the circuit and verify voltage at the element and a heavy current draw with an amp clamp; no draw means an open element, cable, or relay.

  5. 5.Test the element and control wiring

    Check the element for continuity (near 0 ohms is normal) and the ECM control wire for opens before replacing parts.

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