Case IH t5C – Electronic Management Unit (EMU) / Transmission Controller (EDC): Reverse Polarity Of Engine Speed Sensor, Data Valid But Above Normal Range

The Electronic Management Unit (EMU) or Transmission controller is receiving a signal from the engine speed sensor that is valid in its data structure, but the electrical polarity is reversed and the speed data is registering above the normal operating range. This is typically caused by incorrectly pinned/swapped wiring harness connectors, a short circuit, or internal failure of the inductive sensor.

• MXM
• MXM120
• MXM130
• MXM140
• MXM155
• MXM175
• MXM190
• TM115
• TM190

1. 1

   Visual Inspection: Check the sensor and harness connector pins for corrosion, moisture, or pushed-back pins.

2. 2

   Wiring Polarity & Continuity: Verify the wiring harness back to the controller for continuity and shorts to ground. Ensure the two wires have not been swapped or repaired backward, which directly causes the 'Reverse Polarity' condition.

3. 3

   Resistance Test: With the engine stopped and the sensor disconnected at ambient temperature, measure the resistance across the sensor's pins. A healthy inductive speed sensor typically reads approximately 450 Ohms (+/- 20 Ohms).

4. 4

   Voltage Test: While cranking or with the gear turning, check for an alternating voltage (AC) output from the sensor to confirm it is generating a pulse sequence.

1. 1

   Turn off tractor

   Turn off the tractor, engage the parking brake, and disconnect the negative battery cable.

2. 2

   Locate sensor

   Locate the engine speed sensor. On these models, it is typically an inductive proximity sensor positioned on the flywheel bell housing or transmission housing cover.

3. 3

   Disconnect harness

   Disconnect the 2-pin electrical harness plug from the sensor.

4. 4

   Remove sensor

   Remove the retaining bolt holding the sensor in place and carefully pull the sensor out of the housing.

5. 5

   Clean mounting port

   Clean the mounting port on the housing to ensure the new sensor seats at the correct depth (incorrect depth can cause out-of-range readings).

6. 6

   Install new sensor

   Insert the new engine speed sensor and tighten the retaining hardware.

7. 7

   Reconnect harness

   Reconnect the electrical harness, ensuring the plug clicks securely into place and the wiring is not strained.

8. 8

   Reconnect battery

   Reconnect the battery.

9. 9

   Clear fault codes

   Turn the key to the "ON" position and use the tractor's built-in diagnostic system (H-Menu) to clear the stored fault codes.

10. 10

    Verify repair

    Start the engine and verify that the tachometer reads correctly and the t5C code does not return.