Caterpillar Fault Code
Free · no signupE1729 FMI 03
AdBlue Warning / 5 MPH Limp Count
System
Emissions / DEF
Symptom
AdBlue Warning / 5 MPH Limp Count
Diagnosis & fix steps
LOGIC: DEF Tank Level Sensor Circuit High (Resistance Out of Range).
ACTION: Remove multi-function DEF header unit from the tank. Clean crystalline urea buildup from the internal float rail; measure resistance across the ultrasonic/reed sensor circuit.
Red Seal field insights
Urea Baking: In intense open-pit heat, water evaporates from the DEF tank vent, leaving hard crystal crusting that binds the level float at the bottom of the tube.
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