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P codepowertrainMedium severity

P0543Intake Air Heater "A" Circuit Open

The intake air heater circuit is electrically open, so current cannot flow through the heater element or its control circuit at all.

Definition

The ECM checks the intake air heater circuit for continuity and sets P0543 when it detects an open — a broken feed cable, blown fusible link, failed relay, or a burned-out grid element. With no heater operation, the engine suffers extended cranking, hard starting, white smoke, and rough running when cold, and may not start in severely cold weather; the MIL illuminates. Because the heater feed carries very high current, the open is frequently at a heat-damaged connection rather than inside the element itself.

Common causes

  • Burned-out (open) heater grid element
  • Blown fusible link or maxi-fuse in the high-current feed
  • Broken or corroded-through feed cable at the heater or relay stud
  • Failed relay with permanently open contacts
  • Open control wiring between the ECM and relay
  • Loose stud nuts that arced and burned the connection open

Common misdiagnoses

  • Batteries and starter for the hard-start complaint
  • Glow plugs on engines equipped with a grid heater instead
  • Injectors for cold white smoke
  • ECM replacement for a blown fusible link

Troubleshooting steps

  1. 1.Check the fusible link and fuses

    Verify battery voltage is present on the heater feed side of the relay; a dead feed points to a blown link, which itself signals a past overcurrent event.

  2. 2.Ohm the heater element

    Measure across the grid element terminals — expect well under 1 ohm; an open (OL) reading confirms the element has burned through.

  3. 3.Inspect every high-current junction

    Remove and clean the relay and heater stud connections, looking for bluing, melted insulation, and crumbling terminals from arc damage.

  4. 4.Test the relay

    Energize the relay coil and verify continuity across the contacts; replace the relay if the contacts never close.

  5. 5.Verify repair under load

    After repairs, command the heater and amp-clamp the feed to confirm full specified current draw, then torque the stud nuts to spec so they do not loosen again.

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