Case IH 17901 (F-3509-05) - ECU – Engine Control Unit (ECU / ECM): ECU 5 Volt Sensor Supply 1 - Current Below Normal, Open Circuit, or Short to Ground

The Engine Control Unit (ECU) has detected an under-voltage condition on its internal 'Sensor Supply 1' circuit. A shorted sensor or chafed wiring pulls the 5-volt supply down, causing all sensors on this circuit to lose power, resulting in erratic readings, engine derate, or a complete engine stall.

• VESTRUM CVX
• Austoft Series Sugarcane Harvesters (e.g., Austoft 9900)
• Magnum Series Tractors
• Puma Series Tractors
• Farmall Series

1. 1

   Verify that the tractor's battery voltage is healthy and that the ECU is receiving proper primary voltage to rule out false supply codes.

2. 2

   Perform a Sensor Isolation Test (Drop Test): Turn the key ON (engine OFF). Back-probe the 5V supply wire at one of the sensors. Disconnect the sensors on the 'Supply 1' circuit one at a time (typically fuel pressure, oil pressure, and boost/manifold pressure). If the 5-volt reference suddenly returns to normal, the unplugged sensor is internally shorted.

3. 3

   Inspect the engine wiring harness for chafing, melted insulation, or pinch points where the harness routes around the engine block, exhaust components, or frame rails.

4. 4

   Disconnect the main engine harness from the ECU. Check the pins for water intrusion, corrosion, or bent terminals. Test for continuity to ground on the 5V supply pin.

1. 1

   Disconnect Power

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

2. 2

   Repair Wiring

   If a short-to-ground was found in the wiring harness during diagnosis, open the wire loom. Cut out the damaged section of the wire and repair it using OEM-approved methods (rosin-core solder and adhesive-lined heat shrink tubing). Re-loom and secure the harness away from vibration points.

3. 3

   Replace Sensor

   If the isolation test proved a sensor was internally shorted, remove the faulty sensor, clean the mounting port, and install the replacement sensor. Torque to OEM specifications.

4. 4

   Replace the ECU

   If the wiring harness tests perfectly clear of shorts, all sensors are unplugged, and the ECU still fails to output 5 volts on the Supply 1 pin, the ECU's internal power stage driver has failed. Remove the faulty ECU and install a replacement. Note: A new ECU must be flashed/programmed by a dealer with the correct software payload for your specific machine.

5. 5

   Clear Codes

   Reconnect the battery, turn the key ON, and use a diagnostic tool (like the Case IH EST) to clear the inactive fault codes. Run the engine to verify the repair.