Massey Ferguson U 1761 (18) – Engine ECU / SCR (Selective Catalytic Reduction) System Controller: Urea tank error: Tank level VERY low

This code indicates that the DEF (Diesel Exhaust Fluid) / AdBlue level sensor is reporting that the fluid in the tank has dropped below the critical minimum threshold. When this code is active, the machine will typically enter a severe engine derate (reduced power) to comply with emissions regulations until the fluid level is restored or the sensor issue is resolved.

• 8600 Series
• 8650
• 8660
• 8670
• 8680
• 8690
• 8700 series
• 5700/6700 series

1. 1

   Visually inspect the actual fluid level in the DEF tank. If the tank is full but the gauge reads empty, the sensor is at fault.

2. 2

   Check the DEF tank cap and breather. Ensure no vacuum is being created and look for heavy urea crystallization around the sensor head that might be causing the float to stick.

3. 3

   Inspect the wiring harness and the electrical connector at the DEF tank header. Look for corrosion, moisture, or rubbed wires that could cause a loss of signal.

4. 4

   Ensure the DEF fluid is not contaminated with diesel, water, or dirt, which can damage the sensor assembly.

1. 1

   Clean the Area

   Thoroughly clean the exterior of the DEF tank and the area around the DEF header. DEF systems are unforgiving to dirt; treat the tank neck like a jet fuel filler.

2. 2

   Drain the Tank

   Drain or siphon the DEF fluid from the tank into a clean container (if reusing) or dispose of it if contamination is suspected.

3. 3

   Disconnect Lines

   Disconnect the electrical harness connector from the DEF header.

4. 4

   Disconnect Hoses

   Carefully disconnect the heated DEF supply and return lines from the header. These are usually quick-connect fittings. Inspect the O-rings on these lines for nicks.

5. 5

   Remove the Sensor

   Unscrew the retaining ring or mounting bolts securing the DEF header to the tank.

6. 6

   Extract

   Carefully pull the old DEF header/sensor assembly straight up and out of the tank.

7. 7

   Install New Part

   Insert the new DEF header/sensor assembly, ensuring the sealing O-ring is properly seated to prevent leaks and contamination.

8. 8

   Reassemble

   Secure the retaining ring/bolts, reconnect the DEF lines, and plug in the electrical harness.

9. 9

   Refill and Clear

   Refill the tank with fresh, clean DEF. Turn the key on, use a diagnostic tool to clear the U 1761 (18) fault code, and verify that the cab gauge now reads the correct fluid level.