Deutz-Fahr 595 – ECM/ECU (EMR3/EMR4): Fuel Metering Unit Short to Ground

The Engine Control Unit (ECU) has detected an electrical anomaly in the Fuel Metering Unit circuit. This component regulates the fuel supplied to the high-pressure pump in the common rail system. The fault may indicate a short circuit to the positive battery side (FMI 3), a short to ground (FMI 4), an open circuit (FMI 5), or over-temperature (FMI 12). This condition prevents the pump from generating the required fuel rail pressure, leading to rough running, engine surging, hard starting or no-start conditions, reduced power (derate), and decreased fuel efficiency.

• Deutz TCD 2.9 L4
• Deutz TCD 3.6 L4
• Deutz TCD 4.1 L4
• Deutz TCD 2012
• Deutz TCD 2013

1. 1

   Verify the fault code using a diagnostic tool like Deutz SerDia to confirm that fault code 595 (SPN 523615 / FMI 4) is active or stored.

2. 2

   Visually inspect the wiring harness between the engine ECU and the fuel metering unit on the high-pressure pump for chafing, melting, pinched wires, or damage causing a short to the engine block or frame.

3. 3

   Disconnect the electrical connector at the fuel metering unit and inspect the terminals on both the harness side and the valve side for corrosion, moisture, or damage. A known issue with these systems is a poor connection at the pigtail, which can vibrate and cause signal loss or damage to the metering unit itself.

4. 4

   Test the harness for a short to ground: with the ignition OFF and the metering unit disconnected, use a multimeter to check for continuity between the high-side control wire at the harness connector and a known good ground. There should be no continuity.

5. 5

   Test the metering unit resistance: measure the electrical resistance across the two pins of the fuel metering unit. A known good unit should read approximately 3.0 to 3.1 Ohms. A reading near zero indicates an internal short circuit (one forum user reported a reading of 2.5 Ohms on a faulty unit).

6. 6

   For intermittent issues, use an oscilloscope to analyze the Pulse Width Modulated (PWM) signal from the ECU to the metering valve. A signal that is constantly low or shows an abnormal waveform can indicate a problem with the ECU's driver circuit or the valve itself.

1. 1

   Safety First

   Disconnect the negative battery terminal to prevent electrical hazards.

2. 2

   Access the Metering Unit

   Locate the high-pressure fuel pump on the engine. The fuel metering unit (MProp) is the solenoid valve mounted to it.

3. 3

   Perform Diagnostics

   Complete the diagnostic checks outlined to isolate the failure to the wiring or the valve itself.

4. 4

   Repair wiring harness (if applicable)

   If the harness test confirmed a short to ground, repair the damaged section of the wire or replace the engine wiring harness as needed.

5. 5

   Replace metering unit and pigtail (if applicable)

   If the connector is faulty or the valve is internally shorted, replace both the fuel metering unit and the harness connector pigtail. Disconnect the electrical plug and fuel lines (be prepared to catch any residual fuel). Unscrew the mounting bolts, remove the old unit, and ensure the mounting surface on the pump is clean. Install the new metering unit with its O-rings/seals and torque the bolts to the manufacturer's specification. Reconnect the fuel lines. Cut the old plug off and splice the new pigtail connector to the engine harness, ensuring proper wire-to-wire connections and using sealed connectors or heat shrink tubing.

6. 6

   Final Steps

   Reconnect the negative battery terminal. Turn the ignition on (without starting the engine) to allow the fuel system to prime and check for any leaks. Use a diagnostic tool to clear the fault codes from the ECU. Start the engine, monitor its performance, and check for any returning fault codes.