New Holland ENG 121 – Engine Controller / Engine ECU (ENG): Engine Position Sensor / Crankshaft Sensor Failure

The Engine Position Sensor (on 8.3 Liter or 9 Liter engines) or the Crankshaft Sensor (on 15 Liter engines) has failed. The ECM loses synchronization data required to control fuel injection timing, which typically results in a no-start condition, stalling, or the engine running very poorly.

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1. 1

   Check battery voltage to ensure it is at least 12.5V and does not drop below 10.5V during cranking.

2. 2

   Inspect the wiring harness and electrical connector at the sensor for corrosion, backed-out pins, or chafed wires shorting to the engine block.

3. 3

   Test the sensor's internal resistance with a multimeter, or use an oscilloscope to verify the signal waveform while cranking.

4. 4

   Inspect the tone wheel (phonic wheel) on the crankshaft pulley or flywheel for damage, metallic debris, or delamination.

1. 1

   Power Down

   Turn off the ignition and disconnect the negative battery cable to prevent electrical shorts.

2. 2

   Locate the Sensor

   Locate the Engine Position Sensor / Crankshaft Position Sensor. Depending on the engine displacement, it is typically installed on the timing gear case, directly behind the crankshaft pulley, or at the flywheel housing.

3. 3

   Remove the Sensor

   Disconnect the electrical pigtail/connector. Remove the retaining bolt(s) securing the sensor and carefully pull the sensor out of its bore.

4. 4

   Clean the Port

   Wipe the mounting surface and bore clean of any oil, dirt, or rust to ensure the new sensor seats perfectly flat.

5. 5

   Install the New Sensor

   Insert the new sensor. Note: Some of these specific engines require a special alignment tool (e.g., a depth/air-gap setting tool) to ensure the sensor is positioned at the exact distance from the tone wheel.

6. 6

   Reassembly

   Tighten the retaining bolt to the manufacturer's torque specification and plug the electrical connector back in.

7. 7

   Clear Codes

   Reconnect the battery. Use a compatible diagnostic tool (such as the CNH Electronic Service Tool or Jaltest) to clear the ENG 121 fault code from the Engine ECU.