Universal HD Fault Code
Free · no signupSPN 3031 FMI 04
DEF Warning Light / SCR Limp Mode
System
Aftertreatment / SCR
Symptom
DEF Warning Light / SCR Limp Mode
Diagnosis & fix steps
LOGIC: Diesel Exhaust Fluid (DEF) Tank Temperature Sensor Voltage Low.
ACTION: Disconnect combined DEF tank level/temperature/quality header module. Test thermistor resistance across temperature pins; inspect harness routing near the transmission crossmember for chafing to chassis ground.
Red Seal field insights
Freezing Protection: Urea solution freezes at -11°C (12°F); a grounded signal wire simulates extreme tank heat, preventing the ECM from energizing tank heating coolant valves and throwing SCR readiness faults.
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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