John Deere 4334.03 – Engine Control Unit (ECU): DEF Dosing Unit Signal Out of Range High

The Engine Control Unit has detected excessive sensor output from the Diesel Exhaust Fluid (DEF) pressure sensor circuit. The voltage is above the normal operating range, which typically points to a short circuit to a 12-volt source or an open circuit.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5090M
• 5100M
• 5100MH
• 5100ML
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 330G
• 331G
• 332G
• 333G
• 9470RT
• 9520RT
• 9570RT
• 5075M
• 210G
• 210GLC
• 350G LC

1. 1

   Locate the DEF Dosing Unit (B5501) and visually inspect the wiring harness connecting it to the ECU.

2. 2

   Disconnect the harness at the DEF dosing unit and the ECU to check for damaged, bent, or corroded pins.

3. 3

   Use a multimeter to test the DEF pressure sensor circuit for a short to 12V or an open circuit.

4. 4

   Verify that the DEF tank is adequately filled and check the dosing unit and supply lines for leaks or blockages.

5. 5

   Run a DEF quantity test or monitor live pressure sensor data via a diagnostic tool to see if the sensor reading is stuck at a high voltage.

1. 1

   Power Down

   Turn off the engine and disconnect the battery to prevent electrical damage.

2. 2

   Harness Repair

   If the diagnostic checks revealed a short to 12V or a broken wire in the chassis harness between the ECU and the B5501 DEF Dosing Unit, repair the wiring or replace the damaged connector.

3. 3

   Component Replacement

   If the wiring is intact, the fault is internal to the sensor. Depending on the specific engine configuration, replace the standalone DEF Pressure Sensor or the entire DEF Dosing Unit Pump assembly (as the sensor is often integrated into the pump module).

4. 4

   Reassembly

   Reconnect the electrical harnesses and restore battery power.

5. 5

   Clear and Verify

   Connect a diagnostic tool, reset the ECU to clear the 004334.03 fault code, and run the engine. Monitor the DEF system to ensure it primes correctly and maintains the correct pressure without throwing the code.