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P2605Intake Air Heater "A" Circuit/Open

The control module has detected an open circuit in the intake air heater "A" circuit, the electric heater (grid heater) that warms incoming air for cold starts.

Definition

On diesel and some gasoline engines, the ECM energizes an intake air heater element through a relay or solenoid during cold starts and monitors the circuit for current flow and feedback voltage. P2605 sets when the module commands heater "A" on but detects an open circuit or no current draw. Symptoms are mostly cold-weather related: hard starting, extended cranking, white or blue smoke, and rough idle until warm, along with an illuminated MIL that can fail an emissions inspection. In mild temperatures the engine may start and run normally.

Common causes

  • Corroded or burned power stud connections at the heater element (very common on grid-heater diesels)
  • Failed intake air heater relay or solenoid contactor
  • Open (burned-out) heater element
  • Blown fusible link, mega-fuse, or broken feed cable
  • Open in the control or feedback wiring to the ECM
  • Failed ECM driver (rare)

Common misdiagnoses

  • Glow plugs replaced on engines that actually use a grid heater
  • Batteries or starter blamed for hard cold starts
  • Fuel injectors replaced for cold-start white smoke
  • Intake air temperature (IAT) sensor

Troubleshooting steps

  1. 1.Inspect the heater power studs and cables

    Look for melted insulation, green corrosion, or loose nuts at the heater element terminals and relay studs; these high-current joints are the most common failure point.

  2. 2.Check fuses and the power feed

    Verify battery voltage is present at the heater relay input; a blown fusible link or mega-fuse kills the whole circuit.

  3. 3.Measure the element for continuity

    Grid heater elements read well under 1 ohm, so use a continuity/low-ohms check across the element; an open reading means a failed element.

  4. 4.Command the heater with a scan tool

    Activate the intake air heater output and listen for the relay/solenoid click while verifying voltage appears at the element terminal.

  5. 5.Confirm current draw

    With an amp clamp on the feed cable, a healthy grid heater draws heavy current (often 90+ amps per element); little or no draw confirms an open circuit.

  6. 6.Verify the ECM control circuit

    Check the relay control and feedback wires for opens back to the ECM before condemning the module.

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