John Deere 003361.03 – ECU: DEF Injector Voltage Issue

The Engine Control Unit (ECU) has detected a voltage higher than the expected range in the Diesel Exhaust Fluid (DEF) dosing injector circuit. This electrical fault disrupts the proper functioning of the aftertreatment system's emissions control, which can trigger a check engine light, a DEF system warning on the dashboard, and potentially force the engine into a derated mode to prevent further damage.

• 9470RT
• 9520RT
• 9570RT
• 8245R
• 8400R

1. 1

   Inspect the wiring harness and connectors between the ECU and the DEF injector for chafing, corrosion, or loose pins.

2. 2

   Examine the DEF injector nozzle for physical damage or white crystalline deposits, which indicate DEF leakage or an improper spray pattern.

3. 3

   Visually inspect the DEF quality (it should be clear and colorless with a faint ammonia smell). If questionable, verify the urea concentration is between 31.8% and 33.2% using a refractometer (such as John Deere JDG11594 or JDG11684). If out of specification, drain the DEF tank, flush with distilled water, and refill with fresh, high-quality DEF.

4. 4

   With the ignition on, measure the voltage at the DEF injector's power supply wire. Expect approximately 12 volts during scan tool activation; a significantly higher reading confirms the fault.

5. 5

   Disconnect the DEF injector and measure resistance across its terminals. The reading should be between 2 to 10 ohms (specifically 7 ohms for certain models). An out-of-spec reading indicates internal electrical failure.

6. 6

   Perform a Reductant Injection Quantity Test using a diagnostic scan tool to verify output volume (40-55 ml expected over 2 minutes) and observe for a uniform spray pattern.

1. 1

   Prepare for repair and ensure safety

   Wear appropriate personal protective equipment to protect against corrosive DEF. If DEF comes into contact with skin or eyes, flush the area with plenty of water. Ensure the DEF system is thawed (run the engine if frozen) and disconnect the battery before proceeding.

2. 2

   Remove the faulty DEF injector

   Clean the area around the injector to prevent contamination. Disconnect the electrical connector (pull back the two small ears to release on John Deere connectors) and the DEF line, being prepared for some residual DEF to be present. Remove the mounting hardware and extract the injector from the exhaust system.

3. 3

   Install the new DEF injector

   Seat the new DEF injector correctly into the exhaust system. Tighten the mounting hardware to the manufacturer's specified torque, then reconnect the DEF line and the electrical connector.

4. 4

   Prime system and verify repair

   Reconnect the battery. Use a diagnostic scan tool to prime the DEF system and remove any air from the lines. Clear the 003361.03 fault code from the ECU, run the engine to check for leaks, and perform a full duty cycle test drive to ensure the code does not return.