John Deere 5126.03 – ECU (Engine Control Unit): Sensor Supply #8 Voltage Out of Range High

The 5-volt reference circuit (Sensor Supply 8) is experiencing a voltage higher than its upper limit, which typically points to a short circuit to a 12V power source. This affects critical emissions sensors including the DPF Pressure Differential Sensor, DOC/DPF Temperature Sensor, SCR Temperature Sensor, and the DEF Pressure Sensor.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 5085M
• 5095M
• 5105M
• 5115ML
• 8235R
• 8245R
• 8260R
• 8285R
• 8310R
• 8310RT
• 8335R
• 8335RT
• 8360R
• 8360RT
• 8400R
• 9470RT
• 9520RT
• 9570RT
• 6090MC
• 6090RC
• 6100MC
• 6100RC
• 6110MC
• 6110RC

1. 1

   Inspect Wiring and Connections: Visually check the engine wiring harness and connectors associated with Sensor Supply 8 (routing to the DPF, DOC, SCR, and DEF sensors) for damaged, frayed, or loose wires.

2. 2

   Check for Short Circuits: Inspect the circuit for any points where the 5V sensor wires may be rubbing against or touching a 12V power source, causing a short to high voltage.

3. 3

   Test Sensor Elements (Isolation Test): Disconnect the DPF Pressure Differential, DOC/DPF Temperature, SCR Temperature, and DEF Pressure sensors one at a time and monitor the supply voltage; if it returns to 5V, the unplugged sensor is internally shorted.

4. 4

   Verify ECU Electrical Supply: Ensure that the ECU itself is outputting a stable 5V reference voltage when the harness is isolated.

1. 1

   Turn off the engine and disconnect the battery to ensure safety.

   Ensure the machine is powered down before beginning electrical repairs.

2. 2

   Repair or replace damaged wiring.

   If the diagnostic checks revealed damaged wiring (e.g., a short to 12V), repair the affected section of the wiring harness or replace the damaged pigtail connector. Insulate the repair thoroughly.

3. 3

   Replace faulty sensor.

   If a specific sensor was identified as internally shorted during the isolation test, remove the faulty sensor and install a new OEM replacement.

4. 4

   Reconnect all sensor connectors and restore battery power.

   Ensure all connections are secure before restoring power.

5. 5

   Reset the ECU.

   Reset the ECU using a John Deere diagnostic tool (like Service ADVISOR) to clear the 005126.03 fault code.

6. 6

   Start the engine and monitor the system.

   Ensure the code does not return and the sensor supply voltage remains stable at 5V.