Case IH 3955 – ISM-DI: Camshaft Sensor Error - Invalid Signal

The engine control module is receiving an erratic, implausible, or missing signal from the camshaft position sensor, indicating a loss of synchronization or an offset between the camshaft and crankshaft speed sensors, preventing the engine from properly timing fuel injection.

• skid steer
• Farmall 80N
• Farmall 80V
• Farmall 85C
• Farmall 95C
• Farmall 100N
• Farmall 105C
• Farmall 115C
• Quantum 80F
• Quantum 80N
• Quantum 80V
• Quantum 110F
• Quantum 110N
• Steiger
• SR175
• SR250
• SV250
• SV300
• 570NXT

1. 1

   Verify the physical and electronic offset between the camshaft and crankshaft speed sensors to check synchronization

2. 2

   Inspect the crankshaft signal wheel (tone ring) to ensure it is not damaged, loose, or covered in metallic debris

3. 3

   Inspect the wiring harness leading to the camshaft position sensor for chafing, open circuits, or shorts to the battery/ground

4. 4

   If the sensor signal is stuck above the maximum range or below the minimum range and the wiring is intact, verify the engine controller (ECU)

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the negative battery cable.

2. 2

   Locate the Sensor

   Locate the camshaft position sensor on the engine block (typically near the cylinder head or camshaft gear housing).

3. 3

   Remove the Faulty Sensor

   Disconnect the electrical harness connector from the sensor. Remove the retaining bolt(s) and carefully pull the sensor out of its mounting port.

4. 4

   Clean and Inspect

   Wipe the mounting port clean of any oil or debris. Inspect the internal tone ring/gear through the hole for any obvious damage.

5. 5

   Install the New Sensor

   Lubricate the O-ring on the new camshaft position sensor with a small amount of clean engine oil. Insert the sensor into the port and tighten the retaining bolt to OEM torque specifications.

6. 6

   Reconnect

   Plug the electrical harness back into the sensor and reconnect the battery.

7. 7

   Clear Codes

   Turn the ignition on and use a diagnostic scan tool to clear the 3955 fault code. Start the engine and verify that the code does not return and that engine timing/performance is restored.

8. 8

   Replace Engine Controller

   If the sensor and wiring are perfectly functional but the signal remains out of range, replace the Engine Controller.