Case IH 3131 – Engine ECU: Grid Heater Always Switched On

The underlying condition triggering this code is typically a short circuit to ground in the grid heater circuit, a defective grid heater switch, or a grid heater relay/solenoid that has become stuck in the closed position. When the relay sticks closed, it causes an extended on-time of the intake air heater, which can lead to severe overheating of the grid heater element and potential melting of the power connection bolt.

• Magnum series (235–340 Series 4)
• Steiger series
• Quadtrac series
• Puma series (150, 185 CVT)
• Patriot Sprayers (3230)
• 580 Super N Backhoes
• F-Series Wheel Loaders (721F, 1121F)

1. 1

   Check the grid heater switch to verify it is not defective or internally shorted.

2. 2

   Inspect the grid heater relay for welded contacts by testing for continuity across the high-current terminals when the key is off and the coil is unpowered.

3. 3

   Check the wiring harness between the Engine ECU, the relay, and the grid heater for any broken, disconnected, or short-to-ground conditions.

4. 4

   Inspect the intake air heater element and isolated power connection bar for electrical arcing, melting, or debris that could drop into the intake system.

1. 1

   Disconnect Power

   Immediately disconnect the batteries. The grid heater draws massive amperage, and a stuck relay poses a fire hazard and can melt the intake manifold connections.

2. 2

   Locate the Relay

   Locate the grid heater relay/solenoid (often mounted near the battery junction block or engine frame bracket).

3. 3

   Remove the Defective Relay

   Disconnect the electrical connector to the grid heater relay, remove the retaining hardware, and detach the relay.

4. 4

   Repair Wiring

   If the diagnostic checks revealed a short circuit to ground in the wiring harness, repair or replace the affected cable sections.

5. 5

   Replace Damaged Components

   Install a new grid heater relay. If the grid heater element or the power connection cable was damaged by overheating, replace those components as well.

6. 6

   Reassemble and Clear Codes

   Reconnect the battery cables. Use an Electronic Service Tool (EST) to clear the fault code from the Engine ECU and cycle the key to verify the grid heater operates normally (it should only cycle on when temperatures dictate and shut off automatically).