Case IH P5B – Engine Control Unit (ECU) / Electronic Diesel Control (EDC): Reverse Polarity Of Engine Speed Sensor, Data Valid But Below Normal Range

The engine control system is receiving an inverted or incorrect pulse sequence from the engine speed sensor (crankshaft increment sensor). The data being received is technically valid but falls below the normal expected operating range. When this occurs, the system response typically allows the engine to keep running using a backup segment sensor, but a longer cranking/start time is required before the control unit can determine the Top Dead Center (TDC) for ignition.

• MXM
• MXM Series (MXM 120, 130, 140, 155, 175, 190)
• Maxxum series
• Magnum series
• Steiger tractors
• TM Series (TM120 - TM190)
• T-Series tractors

1. 1

   Ensure the power is OFF, the keyswitch is OFF, and the battery is disconnected (or the relevant fuse is pulled)

2. 2

   Disconnect the connectors at both ends of the engine speed sensor circuit to isolate it and prevent false readings

3. 3

   Measure resistance (ohms) using a multimeter from the connector pins to a plated metal chassis ground to ensure resistance is within OEM range and there is no short to ground

4. 4

   Inspect the wiring harness to verify polarity, ensuring the sensor wires were not pinned backward during a previous repair

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the negative battery cable.

2. 2

   Locate the Sensor

   Locate the engine speed sensor (crankshaft speed sensor), typically mounted on the engine block near the flywheel or crankshaft pulley.

3. 3

   Inspect the Harness

   Disconnect the sensor's electrical connector. Inspect the pins for corrosion, damage, or reversed wiring. If the connector was recently replaced, re-pin the connector to the correct polarity.

4. 4

   Remove the Sensor

   If the wiring is correct and tests fine, the sensor itself is likely internally shorted or failing. Remove the mounting bolt securing the sensor and pull it straight out of the block.

5. 5

   Install the New Sensor

   Insert the replacement OEM engine speed sensor. Ensure it is seated flush so the air gap between the sensor and the tone ring is correct. Tighten the mounting bolt.

6. 6

   Reconnect and Calibrate

   Reconnect the wiring harness and battery. Clear the fault codes. Note: If the microprocessor or sensor was replaced, a Transmission/EDC calibration may be required via the H-Menu (using the High and Low range buttons while setting engine speed to 1200 ERPM).