Case IH 3485 – Engine Control Unit (ECU): Engine coolant pump actuator PWM power stage: short to battery.

The Engine Control Unit (ECU) has detected a high voltage condition (short circuit to the battery or an external power source) on the output power stage circuit that controls the Pulse Width Modulation (PWM) actuator for the engine coolant pump.

• Magnum
• Steiger
• Puma
• Optum
• Axial-Flow 7120
• Axial-Flow 7230
• Axial-Flow 7240
• Axial-Flow 8240
• Axial-Flow 9240

1. 1

   Inspect the wiring harness routing from the Engine ECU to the Coolant Pump PWM Actuator for chafed wires rubbing against the engine block, brackets, or hot exhaust components.

2. 2

   Disconnect the plug at the coolant pump actuator and check for water intrusion, corrosion, melted plastic, or bent/pushed-out pins.

3. 3

   With Key ON, Engine OFF, disconnect the harness from the ECU and coolant pump, and test the PWM control circuit wire for continuity to battery positive (B+) using a digital multimeter.

4. 4

   If the wiring harness tests fine, check for an internal short within the electronic circuitry of the coolant pump actuator itself.

1. 1

   Disconnect Power

   Turn off the battery disconnect switch or disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Isolate the Fault

   Based on the diagnostic checks, determine if the fault is in the wiring harness or the actuator.

3. 3

   Repair the Harness

   If a short is found in the wiring, open the wire loom, locate the chafed/melted section, splice in a new section of wire using weather-sealed heat-shrink butt connectors, and re-loom the harness securely away from abrasion points.

4. 4

   Replace the Coolant Pump Actuator

   Drain the engine coolant into a clean drain pan. Disconnect the electrical connector from the pump actuator. Remove the mounting bolts securing the PWM actuator. Clean the mating surface on the engine block. Install the new coolant pump/actuator with a new gasket/O-ring. Torque bolts to OEM specifications.

5. 5

   Reassembly

   Reconnect the electrical harness. Refill the cooling system with the specified OAT coolant and bleed the system of air.

6. 6

   Clear Codes

   Reconnect the battery. Connect the CNH Electronic Service Tool (EST) to clear the inactive 3485 fault code. Run the engine and verify that the pump operates correctly and the code does not return.