Case IH 3478 – Engine Control Unit (ECU): Coolant Pump speed: pump speed too low

The measured coolant pump speed is too low, dropping below the expected threshold. This is typically due to a defective speed sensor or the pump switching into a lower speed stage, and can trigger an active power reduction (limp mode) due to the OBD performance limiter.

• Magnum tractors
• Axial-Flow combines
• excavators
• wheel loaders

1. 1

   Verify if the fault occurred during a normal cold start (clear the code and see if it returns at normal operating temperatures)

2. 2

   Check electrical supply (battery and alternator) as low voltage can cause the pump to operate at a lower speed stage

3. 3

   Inspect the wiring harness and connectors leading to the coolant pump speed sensor for high resistance, shorts, or damage

4. 4

   Test the coolant pump speed sensor to verify if it is failing to send the correct rotational speed signal

5. 5

   Verify Engine ECU functionality to rule out an erroneous fault log

1. 1

   Test the Battery and Alternator

   Ensure the machine is supplying the correct voltage to the engine sensors and the coolant pump.

2. 2

   Inspect the Wiring

   Trace the wiring from the coolant pump speed sensor back to the Engine ECU. Repair any corroded pins, broken wires, or areas with high electrical resistance.

3. 3

   Replace the Speed Sensor

   If the wiring and voltage are correct but the ECU is still not receiving the proper speed signal, replace the defective coolant pump speed sensor.

4. 4

   Inspect/Replace the Coolant Pump

   If the sensor is reading correctly but the pump is physically failing to reach the commanded speed stage, the coolant pump assembly (or its internal drive components) is failing and must be replaced.

5. 5

   Clear Codes

   After repairs, clear the Engine ECU fault codes and run the machine under load to ensure the OBD performance limiter deactivates and the code does not return.