Deutz-Fahr SPN 4334 FMI 5 – MCM2 / MCM2.1 or ACM 2.1: AdBlue Dosing Pump: Short circuit to ground

The engine management system has detected that the control signal current for the DEF (Diesel Exhaust Fluid) supply module/pump motor is below the normal operating threshold, indicating an open circuit or a short circuit to ground in the pump's electrical circuit.

• 6105 TTV
• 6110 TTV
• 6120 TTV
• 6130 TTV
• 6140 TTV
• 6150 TTV
• 6160 TTV
• 6170 TTV
• 6180 TTV
• 6190 TTV
• 7200 TTV
• 7250 TTV
• 7300 TTV
• 7340 TTV
• 9300 TTV
• 9340 TTV
• 9370 TTV
• 9400 TTV

1. 1

   Inspect the wiring harness running from the ACM/MCM to the DEF supply module for chafing, breaks, or melted insulation that could cause a short to ground.

2. 2

   Disconnect the electrical plug at the DEF pump and check for water intrusion, crystallized DEF fluid, or bent/corroded pins (common causes of open circuits).

3. 3

   Using a multimeter, check the supply voltage and ground circuits at the pump connector. Test the signal wire for continuity back to the control module and ensure it is not shorted to the chassis ground.

4. 4

   Measure the internal resistance of the DEF pump motor. If the internal coil is open (infinite resistance) or shorted to the pump housing, the pump has failed internally.

1. 1

   Preparation

   Turn off the tractor ignition, disconnect the battery, and locate the DEF supply module (usually mounted near the DEF tank).

2. 2

   Disconnect Electricals

   Unplug the main electrical harness connector from the DEF dosing pump.

3. 3

   Disconnect Fluid Lines

   Carefully disconnect the DEF suction, pressure, and backflow lines. Note: Have a catch pan ready. Clean any spilled DEF immediately with warm water, as it is highly corrosive to metal components.

4. 4

   Removal

   Unbolt the DEF supply module from its mounting bracket and remove the faulty unit.

5. 5

   Installation

   Mount the new DEF supply module and secure the bolts.

6. 6

   Reconnect Lines

   Reattach the DEF fluid lines, ensuring the quick-connect fittings click securely into place to prevent air leaks (which can cause pressure plausibility faults later).

7. 7

   Reconnect Electricals

   Plug in the electrical connector, ensuring the weather seal is intact.

8. 8

   System Prime & Clear Codes

   Reconnect the battery. Use a diagnostic tool to clear the SPN 4334 FMI 5 fault code. Start the engine and allow the exhaust to warm up (the system typically begins pressurizing the dosing system once the exhaust reaches approx. 120°C / 250°F). Verify that the pump primes, no leaks are present, and the code does not return.