Yanmar CE Fault Code
Free · no signupSPN 520288 FMI 14
DEF Warning Lamp / Active Derate (50%)
System
Emissions / DEF
Symptom
DEF Warning Lamp / Active Derate (50%)
Diagnosis & fix steps
LOGIC: DEF Supply Module Internal Backflow Valve Malfunction.
ACTION: Flush DEF pump dosing head with warm distilled water. Inspect the internal 4/2-way reversing valve for urea crystallization preventing evacuation at key-off.
Red Seal field insights
Purge Failure: At key-off, the DEF pump must reverse rotation to suck fluid out of the lines back into the tank; a failed valve leaves fluid to freeze or crystallize in lines.
Same code keeps coming back?
That's a program problem, not a part problem. Book a 30-minute uptime review with Grant, a Red Seal Heavy Duty Technician.
Read before you touch anything
- This is general reference information, not a repair manual. It is for trained, qualified technicians.
- Fault codes, meanings and procedures vary by model, serial number and software version. Confirm the code and the procedure against the manufacturer's service manual before acting.
- Follow the OEM service manual, torque specs and your site's safety procedures: lockout/tagout, block raised equipment, relieve hydraulic, fuel and air pressure, and let hot systems cool.
- You use this information at your own risk. Adventure Mechanical and AM Fleet Integrity accept no liability for damage, injury, downtime or loss arising from its use.
- Not affiliated with or endorsed by any manufacturer. Brand names are used only to identify the equipment a code applies to.
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