Case IH 3156 – Engine Control Unit (ECU): Intake air heater actuator (grid heater relay) open load error

The Engine Control Unit (ECU) monitors the intake air heater relay control circuit for an open load condition. If the ECU detects an open circuit (broken wire, disconnected plug, or internally failed relay) in the intake air heater relay control circuit, this fault is triggered.

• Steiger T4B
• Puma series (150, 165, 180, 195, 210, 225 CVX, 185 CVT)
• Magnum series (235-340)
• Farmall 115U
• STX450
• 240 Series Axial-Flow Combines
• Case 580 Super N backhoes

1. 1

   Verify that the tractor's battery power supply has not been connected to an external power supply (like a jump starter or external charger), which can trigger false codes.

2. 2

   Check for accompanying codes like 3154 (short to battery) or 3155 (short to ground) which indicate a wiring harness short rather than a failed relay.

3. 3

   Inspect the wiring harness between the ECU and the intake air heater relay for broken, chafed, or disconnected wires.

4. 4

   Test the intake air heater relay (grid heater relay) for proper resistance. An infinite resistance reading across the control terminals indicates an internal open circuit.

1. 1

   Turn off the machine and disconnect any external power supplies.

2. 2

   Locate the intake air heater relay (grid heater relay) in the engine compartment.

3. 3

   Disconnect the electrical connector to the grid heater relay.

4. 4

   Inspect the connector pins for corrosion, pushed-out pins, or damage.

   Repair the connector or wiring harness if a physical break is found.

5. 5

   Detach the mounting hardware and remove the faulty grid heater relay.

   Perform this if the wiring is intact and the relay failed the continuity test.

6. 6

   Install the replacement intake air heater relay and secure the mounting hardware.

7. 7

   Reconnect the electrical connector to the relay.

8. 8

   Clear the fault codes via the diagnostic menu or service tool, and cycle the key to verify the code does not return.

   Test cold-start functionality if conditions permit.