New Holland NH 3091 – Engine Control Module (ECM / Engine ECU): Segment speed signal - SOURCE LOW

This code indicates that the engine control module is receiving an abnormally low voltage, an invalid signal, or detecting a reversed connection from the segment speed sensor (which functions as the camshaft position/engine speed sensor). This prevents the module from accurately determining the engine's rotational position and speed.

• T9.390
• T9.450
• T9.505
• T9.560
• T9.600
• T9.645
• T9.700
• TJ275
• TJ325
• TJ375
• TJ425
• TJ450
• TJ500
• T6010
• T6020
• T6030
• T6040
• T6050
• T6060
• T6070
• T6080
• T6090
• TM110 through TM190
• TS100A through TS135A
• T4.95V
• T4040
• T5040
• T5050
• T5060
• T5070

1. 1

   Inspect the wiring harness leading to the engine speed/camshaft position sensor for chafing, breaks, or a short to ground (which causes the 'Source Low' condition).

2. 2

   Disconnect the sensor and check the connector for corrosion, moisture, or backed-out pins.

3. 3

   Verify that the sensor connections have not been reversed during a previous repair, as the code specifically flags 'reversed connections' as a trigger.

4. 4

   Check the sensor mounting for looseness or built-up metallic debris on the magnetic tip that could affect the reading gap.

5. 5

   Test the sensor's voltage supply and resistance with a multimeter to ensure it is receiving the correct reference voltage from the ECM and is within OEM specifications.

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical shorts.

2. 2

   Locate the Sensor

   Locate the segment speed sensor (camshaft/engine speed sensor) on the engine block (location varies slightly by engine model, typically near the timing gear housing).

3. 3

   Disconnect

   Unplug the electrical harness connector from the sensor.

4. 4

   Remove

   Remove the retaining bolt securing the sensor to the engine block.

5. 5

   Extract

   Carefully pull the old sensor out of its mounting port. If it is stuck, twist gently—do not pry aggressively to avoid breaking the tip off inside the engine.

6. 6

   Clean

   Clean the mounting surface and ensure no dirt or debris falls into the engine port.

7. 7

   Install

   Insert the new OEM engine speed sensor. Tighten the retaining bolt to the manufacturer's specified torque.

8. 8

   Reconnect

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

9. 9

   Restore Power

   Reconnect the battery cable.

10. 10

    Clear Codes

    Use a diagnostic tool (or CAN-bus DTC eraser) to clear the NH 3091 fault code from the Engine ECU.

11. 11

    Test

    Start the engine and verify that the code does not return and that the engine RPM reads smoothly without hesitation.