Case IH P4C – Engine Control Unit (ECU / EDC): Coolant Temperature Sensor, Shorted To Low Source

The voltage signal from the Engine Coolant Temperature (ECT) sensor has dropped below the minimum acceptable threshold. In a 5-volt reference circuit, a 'short to low source' means the signal wire is shorting directly to ground (0 volts). This is typically caused by a chafed wire touching the engine block, a melted connector, or the sensor itself failing by internally shorting out.

• MXM
• Case IH MXM Series (120, 130, 140, 155, 175, 190)
• Case IH Puma Series (170, 185, 200, 215, 230 CVX)
• Case IH Magnum Series
• Case IH Steiger Series

1. 1

   Visual Wiring Inspection: Trace the wiring harness from the coolant temperature sensor back to the ECU. Look for chafed insulation, pinched wires, or areas where the harness may have melted against the exhaust or engine block (causing a short to ground).

2. 2

   Connector Check: Disconnect the sensor. Inspect the pins for corrosion, moisture, or damage.

3. 3

   Sensor Resistance Test: Use a multimeter to measure the resistance across the sensor's pins. According to CNH F5 engine service data, a healthy sensor should read specific resistance values based on temperature (e.g., ~7500 ohms at 32°F/0°C, ~500 ohms at 176°F/80°C, and ~280 ohms at 212°F/100°C). If the multimeter reads near 0 ohms, the sensor is internally shorted and must be replaced.

4. 4

   Voltage Check: With the sensor disconnected and the key in the ON position (engine off), check the harness connector for a 5V reference signal from the ECU.

1. 1

   Prep the Machine

   Turn off the tractor, remove the key, and allow the engine to cool completely to avoid severe burns from pressurized coolant.

2. 2

   Locate the Sensor

   The ECT sensor is typically threaded into the thermostat housing or the cylinder head (on some MX/MXM models, it is located above the injection pump on the left side of the engine).

3. 3

   Drain/Catch Coolant

   Place a clean catch pan directly beneath the sensor area. You do not need to drain the entire radiator, but removing the sensor will release some coolant.

4. 4

   Remove the Sensor

   Disconnect the electrical pigtail. Use a deep socket or wrench to carefully unthread the faulty sensor from the block.

5. 5

   Install the New Sensor

   Apply a liquid thread sealant or Teflon tape to the threads of the new sensor (if it doesn't come with pre-applied sealant). Thread it in by hand to prevent cross-threading, then tighten to OEM specifications.

6. 6

   Reassembly

   Reconnect the electrical harness, ensuring the locking tab clicks into place.

7. 7

   Refill Coolant

   Top off the engine coolant reservoir to replace whatever was lost during the swap.

8. 8

   Clear Codes

   Turn the key to the ON position. The active T4C (P4C) code should move to an inactive state or clear entirely from the digital display once the ECU detects the proper voltage range.