Case IH P4B – Engine ECU (Electronic Diesel Control / EDC): Coolant Temperature Sensor, Open Circuit Or Current Below Normal Range

The control module has detected an Open Circuit or Current Below Normal Range in the Engine Coolant Temperature Sensor circuit, indicating the controller is not receiving a valid signal from the sensor due to a disconnected plug, broken wire, corroded connector, or failed sensor.

• MXM
• MXM Series
• MXM120
• MXM130
• MXM140
• MXM155
• MXM175
• MXM190
• Magnum Series
• 235
• 250
• 280
• 310
• 340
• 380
• Steiger/Quadtrac Series
• 350 to 620
• Farmall Series
• 85C
• 95C
• 105U
• 115U
• Axial-Flow Series
• 5140
• 6140
• 7120
• 7240
• 8010
• 8240
• 9240
• Patriot Series
• 4430
• 4440

1. 1

   Visual Inspection: Check the sensor connector and the wiring harness leading back to the ECU. Look for rubbed-through insulation, broken wires, or heavy corrosion inside the plug.

2. 2

   Resistance Test: Disconnect the sensor and measure its internal resistance with a multimeter. The sensor should read approximately: 20°C (68°F) = 4,200 Ω, 40°C (104°F) = 900 Ω, 60°C (140°F) = 780 Ω, 80°C (176°F) = 500 Ω, 100°C (212°F) = 280 Ω. (If the sensor reads completely open/infinite resistance, it has failed internally).

3. 3

   Voltage Check: Turn the key to the ON position (engine off) and probe the harness-side connector. You should see a 5V reference signal coming from the ECU. If there is no voltage, the issue is in the wiring harness or the ECU itself.

1. 1

   Cool Down

   Ensure the engine is turned off and has completely cooled down to prevent severe burns from pressurized, hot coolant.

2. 2

   Locate the Sensor

   Find the coolant temperature sensor, typically threaded into the engine block or thermostat housing.

3. 3

   Prep for Spillage

   Place a clean catch pan directly beneath the sensor area to catch any coolant that escapes during the swap.

4. 4

   Remove the Sensor

   Disconnect the electrical pigtail. Use a deep socket or wrench to unthread the old sensor from the housing.

5. 5

   Install the New Sensor

   Thread the new OEM sensor into the housing. According to the NEF Engine Service Manual, the M14 coolant temperature sensor should be torqued to 17 - 23 Nm (12.5 - 17.0 lb ft).

6. 6

   Reconnect

   Plug the electrical connector back in, ensuring it clicks and locks securely.

7. 7

   Refill and Test

   Top up the engine coolant to the correct level. Start the engine, check the sensor area for leaks, and verify on the display panel that the T4B fault code has cleared.