John Deere 637.1 – Engine Control Unit (ECU): Crankshaft Position Sensor Signal Rate of Change Abnormal

The controller has detected an improper pattern, extra pulses, or electrical noise in the crankshaft speed/position signal. This irregularity can lead to incorrect engine timing, misfires, hard starting, or a derated engine performance condition.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5065M
• 5075M
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5095M
• 5095MH
• 5105M
• 5015ML
• 5090M
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 5200-5520
• 8230
• 9200
• 9300
• 9400
• 319D
• 328D
• 750J
• 850J
• 310G
• 744H
• 670D
• 872D
• 70-series
• 9770
• 3520 Sugar Cane Harvester

1. 1

   Inspect the wiring harness and connector between the ECU and the crankshaft position sensor for open circuits, shorts to ground, high resistance, corrosion, or moisture.

2. 2

   Perform a sensor swap test: if the engine uses identical sensors for the camshaft and crankshaft, swap them. If the fault code changes to 636.10 (Camshaft), the sensor itself is verified as the point of failure.

3. 3

   Check the tone wheel (timing gear) for damage, missing teeth, or looseness by gently prying with a small screwdriver to ensure it hasn't slipped or moved out of sync.

4. 4

   In extreme cases (notably documented on 70 Series combines with 8.1L/9.0L engines), check for severe mechanical failure such as a broken crankshaft at the #6 connecting rod journal if the sensor and wiring are perfectly fine.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the battery to prevent electrical shorts and ensure safety.

2. 2

   Locate the Sensor

   Locate the crankshaft position sensor on the engine block (usually near the crankshaft pulley or flywheel housing, depending on the engine model).

3. 3

   Inspect and Clean

   Disconnect the electrical connector. Clean the contacts with electrical contact cleaner. Inspect the wiring for chafing or breaks. If the harness is damaged, repair or replace the affected section.

4. 4

   Remove the Sensor

   Unbolt and remove the crankshaft position sensor. Inspect the magnetic tip for metal shavings or physical damage, which can cause signal noise.

5. 5

   Replace the Sensor

   If the sensor failed the swap test or is physically damaged, install a new OEM crankshaft position sensor.

6. 6

   Reassemble

   Reconnect the wiring harness securely.

7. 7

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a diagnostic tool (like Service ADVISOR) to clear the ECU fault codes. Start the engine to verify the repair and ensure the code does not return.