SDLG Fault Code

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SPN 3226 FMI 04

Amber DEF Lamp / 30% Engine Torque Derate

System

Aftertreatment / SCR

Symptom

Amber DEF Lamp / 30% Engine Torque Derate

Diagnosis & fix steps

LOGIC: Tailpipe Outlet NOx Sensor Circuit Voltage Low (Short to Ground). ACTION: Disconnect downstream NOx sensor control box at exhaust stack. Check 24V supply and ground; inspect sensor wiring harness where it runs past the turbo heat shield for melted insulation.

Red Seal field insights

Thermal Exhaust Melting: High working exhaust temperatures radiate past loose heat shields, melting the nylon outer braid of the NOx probe harness directly onto the downpipe.

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.

Book an uptime review

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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