Case IH 2949 (3510.04) - DEC – Engine Control Unit (ECU) / DEC: Battery 5V reference 2 circuit low

The control module has detected the voltage on the 5-volt sensor supply circuit #2 has dropped below the acceptable specification. This almost always indicates a short to ground somewhere in the 5V reference #2 circuit, which can be caused by a damaged wiring harness or an internally shorted sensor pulling the voltage down.

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1. 1

   Check for Multiple Codes: Verify if other fault codes are present. If multiple sensor codes are active simultaneously, it strongly points to a shared 5V reference circuit issue rather than a single failed sensor.

2. 2

   Sensor Isolation Test: Disconnect sensors one at a time. If the fault code changes from Low (FMI 4) to High (FMI 3) or the 5V supply returns to normal on your multimeter, the sensor you just disconnected is internally shorted to ground.

3. 3

   Harness Inspection: If disconnecting the sensors does not restore the 5V reference, inspect the engine wiring harness between the ECU and the sensors. Look for chafed wire insulation, pinched wires, or areas where the harness is rubbing against the engine block or chassis, causing a short to ground.

4. 4

   ECU Pin Check: Disconnect the ECU harness and inspect the pins for the 5V supply circuit. Look for bent pins, moisture intrusion, or corrosion.

1. 1

   Power Down

   Turn off the machine, engage the parking brake, and disconnect the negative battery terminal to prevent electrical spikes during repair.

2. 2

   Replace Shorted Sensor

   If the sensor isolation test identified a specific sensor pulling the 5V circuit down, remove the faulty sensor and install a new OEM replacement.

3. 3

   Repair the Wiring Harness

   If a short to ground was found in the wiring harness, carefully open the wire loom. Cut out the damaged section of the wire, splice in a new section using proper solder and heat-shrink tubing, and re-loom the harness securely away from vibration points.

4. 4

   Reassemble

   Reconnect all sensor connectors and the ECU harness. Ensure all connections click into place and are locked.

5. 5

   Clear Codes

   Reconnect the battery. Turn the ignition key to the ON position (do not start). Use the Case IH Electronic Service Tool (EST) or an equivalent diagnostic scanner to clear the inactive fault codes.

6. 6

   Verify Repair

   Start the engine and monitor the dashboard or diagnostic tool to ensure the 3510.04 / 2949 code does not return and the engine operates without derating.