Case IH 3089 (F-637-02) – Engine Control Unit (ECU): Crankshaft speed sensor pattern is not plausible

The Electronic Control Unit (ECU) evaluates the signals received from both the camshaft and crankshaft speed sensors to determine engine angle, speed, and signal quality. If the ECU detects that more than 80 crankshaft signal plausibility errors have occurred, or if the signal is interrupted, out of phase, or missing entirely, this fault is logged. When this happens, the engine may enter a BACKUP mode where it relies solely on the camshaft speed sensor to keep the engine running, often resulting in reduced power or rough running.

• VESTRUM CVX
• Farmall series (40, 45, 50, 85, 90, 95, 105, 110, 120, 130, 140)
• Maxxum series (100 through 150)
• Puma series (130 through 240)
• MX series (MX210, MX230, MX255, MX285, MXU100, MXU135)
• Steiger models
• 240 Series Axial-Flow Combines
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Verify external power: Check that the tractor battery has not been connected to an external power supply (like a booster). If it is, disconnect it and test the system for normal operation, as voltage irregularities can trigger this code.

2. 2

   Inspect wiring and connectors: Inspect the wiring harness and the connector portion of the crankshaft speed sensor for damaged isolation, short circuits to the battery negative/positive terminals, or open circuits.

3. 3

   Perform a resistance test: With the ignition switch OFF, disconnect the sensor. Using a multimeter, measure the resistance across the sensor pins (typically pins 1 and 2). A healthy sensor should read between 750 - 1000 Ω.

4. 4

   Perform an output voltage test: Connect a breakout test lead to the sensor. Start the engine and measure the AC voltage using a multimeter across the leads to verify if the sensor is generating a high-frequency timing signal.

5. 5

   Check mechanical phase: Ensure the camshaft signal wheel and engine crankshaft signal wheel are in their correct positions and not physically out of phase.

1. 1

   Turn off ignition and disconnect battery

   Turn off the ignition and disconnect the machine's battery to prevent electrical shorts.

2. 2

   Locate crankshaft speed sensor

   Locate the crankshaft speed sensor. It is positioned directly over the engine flywheel ring gear case or the engine block timing port matrix.

3. 3

   Disconnect electrical connector

   Disconnect the electrical wiring harness connector from the sensor.

4. 4

   Remove retaining bolt

   Remove the retaining bolt holding the sensor in place (typically an M6 screw).

5. 5

   Remove faulty sensor

   Pull the faulty crankshaft speed sensor out of the engine block.

6. 6

   Insert new sensor

   Insert the new OEM replacement sensor.

7. 7

   Install retaining screw

   Install the retaining M6 screw and torque it to 6 - 10 Nm (4.4 - 7.4 lb ft) as per the service manual.

8. 8

   Reconnect electrical connector

   Reconnect the electrical connector securely.

9. 9

   Clear fault codes

   Reconnect the battery, turn on the ignition, and use an Electronic Service Tool (EST) or diagnostic scanner to clear the inactive fault codes.

10. 10

    Verify repair

    Start the engine to verify the code does not return and the engine runs smoothly without defaulting to backup mode.