John Deere 637.02 – ECU: Crankshaft Position Signal Invalid

The controller detects excessive electrical noise, erratic data, or extra pulses on the crankshaft position sensor input circuit, preventing it from accurately determining engine speed and piston position. This can cause the engine control system to alter ignition timing, reduce engine power (derate by up to 50%), or cause the engine to stall and refuse to restart.

• 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
• 8R Series
• 9230
• 9330
• 9430
• 9530
• 9630
• 450J
• 550J
• 650J
• 750J
• 850J
• 670D
• 672D
• 770D
• 772D
• 870D
• 872D
• G-Series excavators
• 310G
• 310J
• 310K
• skid steers

1. 1

   Inspect the wiring harness between the Crankshaft Position Sensor and the ECU for chafing, bare wires, or melting that could introduce electrical noise or a short circuit.

2. 2

   Check the sensor connector by disconnecting it and inspecting the pins for corrosion, moisture, or loose terminals (poor pin tension).

3. 3

   Verify the sensor is securely bolted to the engine block, as a loose sensor will vibrate and generate erratic extra pulses.

4. 4

   Check cam/crank sync to see if the camshaft sensor is also throwing codes (e.g., SPN 636), which would point to a larger mechanical timing issue rather than a single failed sensor.

1. 1

   Power Down

   Turn off the machine and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Locate the Sensor

   Locate the crankshaft position sensor on the engine block, typically positioned near the crankshaft pulley or the flywheel housing.

3. 3

   Disconnect

   Unplug the 2-pin or 3-pin electrical connector from the sensor.

4. 4

   Remove

   Remove the single retaining bolt holding the sensor in place and carefully pull the sensor straight out of its bore.

5. 5

   Clean and Inspect

   Wipe the mounting port clean. Inspect the tip of the old sensor for physical damage (which could indicate debris in the housing or a damaged reluctor wheel).

6. 6

   Install

   Insert the new OEM crankshaft position sensor. Fasten the retaining bolt to the manufacturer's specified torque.

7. 7

   Reconnect

   Plug the electrical connector back in, ensuring it clicks and locks securely.

8. 8

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a diagnostic scan tool to clear the 000637.02 / SPN 637 FMI 2 fault code. Start the engine to verify the repair.