Deutz-Fahr 1128 – EMR4 ECU: DEF Pump Pressure Sensor Voltage Low

The EMR4 Engine Control Unit has detected that the voltage signal from the Diesel Exhaust Fluid (DEF) pump pressure sensor is below the expected operational range (SPN 523632 FMI 4). This indicates a potential short circuit to ground or a failing sensor within the Selective Catalytic Reduction (SCR) system, preventing accurate DEF pressure monitoring.

• Agrotron 6 Series TTV
• Agrotron 7 Series TTV
• Deutz TCD 2.9 L4
• Deutz TCD 3.6 L4
• Deutz TCD 4.1 L4
• Deutz TCD 6.1 L6
• Deutz TCD 7.8 L6

1. 1

   Inspect the wiring harness leading to the DEF pump module for rubbing, chafing, or damage, especially in the last few inches near the pump connector

2. 2

   Disconnect and inspect the electrical connector at the DEF pump module for corrosion, bent pins, or moisture intrusion

3. 3

   Check the DEF tank and lines for signs of contamination (e.g., diesel fuel or coolant) or crystallization

4. 4

   Verify that only API-certified DEF meeting the ISO 22241 standard is being used

1. 1

   Test sensor voltage

   Using a multimeter, back-probe the signal wire of the DEF pump pressure sensor at the pump module connector with the ignition on. A reading near zero or significantly below specification confirms the 'voltage below normal' condition.

2. 2

   Check for short to ground

   With the sensor disconnected, use a multimeter to check for continuity between the sensor's signal wire in the harness and chassis ground. If continuity exists, locate and repair the short circuit in the wiring harness.

3. 3

   Inspect DEF filters

   Check the main filter in the DEF pump and the suction filter in the tank. While clogged filters typically set a different code, they can lead to low pressure and should be ruled out.

4. 4

   Verify pressure with manual gauge

   Connect a manual pressure gauge to the DEF line. Run a system test or prime the pump and compare the manual gauge reading (typically around 145 PSI) to the pressure value reported by the diagnostic software.

5. 5

   Replace DEF pump module

   If the wiring is intact, manual pressure is normal, but the sensor still reports low pressure, replace the DEF pump module. The pressure sensor is typically integrated into the module and not sold separately.