Caterpillar Fault Code
Free · no signup3427-5
Active Regen Disabled / E1025 Derate.
System
Aftertreatment (DEF)
Symptom
Active Regen Disabled / E1025 Derate.
Diagnosis & fix steps
LOGIC: Aftertreatment Fuel Pump Relay Control: Current Below Normal.
ACTION: Check the 10A ARD fuel pump fuse. If intact, check for 24V supply at the relay socket and verify resistance across the relay control coil (pins 85/86).
Red Seal field insights
System Logic: The ECM sends a ground command to close this relay and trigger the ARD combustion pump. An FMI 5 means the ECM detects an open circuit/broken wire in that command loop.
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