Case IH 3143 – Engine Control Module (ECM): Grid Heater Switch Off Test (Voltage Drop Too High)

This code indicates a malfunction in the intake air heater (grid heater) circuit. The engine control module runs a diagnostic test when commanding the grid heater relay to turn OFF. If the system detects that the voltage drop across the circuit is too high during this 'off' state, it triggers this code. This typically means the grid heater relay is stuck in the closed (ON) position, there is a short to ground in the wiring, or there is excessive resistance in the high-current circuit.

• Case IH Magnum 235 (Series 4)
• Case IH Magnum 260 (Series 4)
• Case IH Magnum 290 (Series 4)
• Case IH Magnum 315 (Series 4)
• Case IH Magnum 340 (Series 4)
• Case IH Farmall 115U

1. 1

   Check for Battery Drain: Check if the batteries are draining quickly when the machine is off, indicating a heavy parasitic draw from a stuck relay.

2. 2

   Inspect the Relay: Feel the grid heater relay and high-current cables; if they are hot to the touch while the engine is off, the relay is stuck closed.

3. 3

   Test Relay Continuity: Disconnect batteries, remove high-current cables, and test for continuity across the two large terminals. Continuity while de-energized means internal contacts are welded shut.

4. 4

   Inspect Wiring: Check the heavy-gauge wire running from the relay to the intake grid heater for chafing, melted insulation, or a short to ground.

1. 1

   Disconnect Power

   Turn off the ignition and completely disconnect the negative battery cables. Warning: Do not skip this step, as the grid heater circuit is wired directly to battery power and can cause severe burns or electrical arcs.

2. 2

   Remove the Faulty Relay

   Unbolt the high-current cables from the large terminals on the grid heater relay. Then, unplug the smaller control wire harness connector.

3. 3

   Dismount the Relay

   Remove the mounting bolts securing the relay to its bracket and remove the unit.

4. 4

   Inspect the Grid Heater Element

   Because a stuck relay leaves the heater on continuously, inspect the intake manifold grid heater terminal. Ensure the plastic insulators are not melted and the terminal is tight.

5. 5

   Install the New Relay

   Mount the replacement relay to the bracket.

6. 6

   Reconnect Wiring

   Reattach the small control harness. Reconnect the heavy-gauge cables to the large terminals and torque the retaining nuts to the manufacturer's specification.

7. 7

   Restore Power and Clear Codes

   Reconnect the battery cables. Turn the ignition ON, use a diagnostic scan tool to clear fault code 3143, and cycle the key to verify the code does not return.