Casagrande Fault Code

Free · no signup

SPN 4334 FMI 18

AdBlue Light / Active Torque Derate

System

Emissions / DEF

Symptom

AdBlue Light / Active Torque Derate

Diagnosis & fix steps

LOGIC: DEF Dosing Unit Reagent Pressure Below Target Limit. ACTION: Clean/replace DEF tank suction strainer screen. Inspect dosing line for urea crystallization or pinched hoses. Test DEF pump delivery pressure (~9 bar).

Red Seal field insights

Fluid Physics: Restricted suction flow drops supply pressure to the dosing injector, preventing proper exhaust NOx reduction and triggering derate.

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.

Track this across your whole fleet

This code is free to read. AM Fleet Integrity lets your team log fault codes against assets, plus the full fault-code library, QR operator reporting, PM scheduling and predictive alerts. Start free — no credit card required.

Start your free trial

Related Casagrande fault codes

← All Casagrande fault codes