John Deere 5435.06 – ECU: DEF Dosing Unit Pump Circuit Has Low Resistance

The resistance in the Diesel Exhaust Fluid (DEF) dosing unit pump circuit has dropped below the acceptable threshold, indicating a short to ground in the circuit powering the DEF pump motor. This prevents the pump from building necessary pressure to inject DEF, eventually leading to engine derate modes.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6105M
• 6140M
• 7210R to 7290R
• 8245R to 8400R
• 9470RT
• 9520RT
• 9570RT
• 350G LC
• Vermeer D24x40 S3
• Vermeer D40x55 S3

1. 1

   Inspect the wiring harness running from the Engine ECU to the DEF Dosing Unit Pump for chafing, melted insulation, or rubbing against the frame or hot exhaust components.

2. 2

   Disconnect the plug at the DEF pump and the ECU to inspect the pins for corrosion, moisture intrusion (DEF fluid wicking), or bent pins.

3. 3

   Using a multimeter, test the DEF pump power and ground circuits for continuity to the chassis ground. Continuity to ground on the power supply wire while disconnected at both ends indicates a shorted harness.

4. 4

   Measure the internal resistance across the pins of the DEF Dosing Unit Pump itself. A reading near zero ohms indicates an internal short and a failed pump motor.

1. 1

   Disconnect Power

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Repair Wiring

   If the diagnostic tests revealed a short in the wiring harness, repair the damaged section of the wire using weather-sealed heat-shrink connectors, or replace the affected harness section.

3. 3

   Replace the DEF Dosing Unit Pump

   If the pump has failed internally, locate the DEF pump assembly, clean the area, disconnect the electrical connector, relieve residual pressure, and disconnect the DEF supply and dosing lines. Unbolt and remove the pump, install the new pump, torque mounting bolts to OEM specifications, and reconnect the lines and harness.

4. 4

   Prime and Clear Codes

   Reconnect the battery, turn the key to the ON position to allow the system to prime, use a John Deere Service ADVISOR diagnostic tool to clear the 005435.06 fault code, and run a forced DEF system test/dosing test to verify operation.