John Deere 5125.04 – ECU: Sensor Supply Voltage Too Low Manifold Air Pressure, Crank Case Pressure, EGR Flow Meter (ECU)

The 5-volt reference voltage on Sensor Supply Circuit #7 has dropped below the acceptable lower limit. This is almost always caused by a short circuit to ground.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5090M
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 9470RT
• 9520RT
• 9570RT
• F4365 AirBoom
• 310K
• 310L
• 544K
• 210G

1. 1

   Turn the ignition to the ON position without starting the engine (Key ON, Engine OFF).

2. 2

   Disconnect the Manifold Air Pressure (MAP) sensor, Crankcase Pressure sensor, and EGR Flow Meter / EGR Temperature sensor one at a time to isolate an internal short.

3. 3

   Monitor the fault code or 5V supply voltage with a multimeter as each sensor is unplugged. If the voltage returns to normal or the code goes inactive, the unplugged sensor is internally shorted.

4. 4

   If all sensors are unplugged and the voltage remains low, inspect the wiring harness between the ECU and the sensors for chafing, melted insulation, or rubbing against the engine block or frame.

1. 1

   Disconnect Battery

   Always disconnect the negative battery terminal before repairing wiring or replacing sensors to prevent ECU damage.

2. 2

   Repair Wiring

   If a harness short was found during diagnostics, repair the damaged wire using OEM-approved heat-shrink butt connectors, or replace the affected harness section. Reroute the harness away from sharp edges or high-heat sources.

3. 3

   Replace Shorted Sensor

   If a sensor was identified as the culprit, remove the faulty sensor. Clean the mounting port to ensure a good seal, and install the new sensor.

4. 4

   Reassemble and Clear Codes

   Reconnect all sensors and the battery. Turn the key ON and use a diagnostic tool (like John Deere Service ADVISOR) to clear the stored 005125.04 fault code.

5. 5

   Test Run

   Start the engine and verify that the code does not return and that the engine operates without derating.