Universal HD Fault Code
Free · no signupSPN 1761 FMI 01
Flashing DEF Lamp / Impending Speed Derate
System
Aftertreatment / SCR
Symptom
Flashing DEF Lamp / Impending Speed Derate
Diagnosis & fix steps
LOGIC: Diesel Exhaust Fluid (DEF) Tank Level Critically Low.
ACTION: Verify actual fluid level in DEF tank. If tank is full, remove the in-tank suction/sender header assembly. Clean crystallized urea scale from magnetic reed/ultrasonic sensor tube; inspect connector pins for blue-green urea corrosion.
Red Seal field insights
The Header Crystal Trap: High-humidity or dirty tank environments cause urea crystals to bridge the level sensor tube or freeze float movement at the bottom of the stem, reporting an empty tank to the ECM despite being filled.
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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