Case IH 3155 (DTC 7C14) - ECU – Engine Control Unit (ECU): Intake air heater actuator is shorted to ground

The control module monitors the intake air heater relay control circuit and has detected that the voltage is bleeding off directly to the chassis ground. This prevents the grid heater from operating correctly, which can lead to hard starting and excessive white smoke in cold conditions.

• MAXXUM T4E
• 240 Series Axial-Flow Combines
• Magnum 235–340 (Series 4)
• Puma Series (e.g., 175, 185 CVT)
• Steiger series
• Farmall models
• Patriot Sprayers (e.g., 3230)
• Case 580N
• Case 580SN
• Case 590SN Backhoes

1. 1

   Check if the tractor battery power supply has been connected to an external power supply (like a jump box or charger). If connected, disconnect it and test for normal operation.

2. 2

   Inspect the wiring harness between the Engine ECU and the grid heater relay for chafed insulation, melted wires, or pinch points shorting to the metal chassis.

3. 3

   Disconnect the grid heater relay and test it with a multimeter to see if the internal coil has shorted to its own casing/ground.

4. 4

   Inspect the ECU connectors for water ingress, corrosion, or bent pins that could be bridging the circuit to a ground pin.

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical arcing.

2. 2

   Locate the Relay

   Locate the intake air heater relay (grid heater relay) in the engine bay. It is typically mounted on an engine frame bracket or near the intake manifold.

3. 3

   Isolate the Short

   Disconnect the electrical connector from the relay. Using a digital multimeter, check the harness side of the connector for continuity to ground. If the harness is shorted: Trace the wiring back to the ECU, locate the damaged section of the wire, and repair it using heat-shrink butt connectors or replace the harness section. If the harness is fine: The short is likely internal to the relay itself.

4. 4

   Remove the Faulty Relay

   Detach the grid heater relay by removing its retaining bracket/hardware.

5. 5

   Install the New Part

   Mount the replacement grid heater relay and securely reconnect the electrical harness.

6. 6

   Reassemble and Clear Codes

   Reconnect the negative battery cable. Turn the ignition to the ON position, use a diagnostic tool to clear the 3155 / 7C14 fault code, and start the engine to verify the code does not return.