Cummins Fault Code

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SPN 157 FMI 18

Derate (5 mph / 8 kph). The truck is restricted to "crawl" speed.

System

Emissions

Symptom

Derate (5 mph / 8 kph). The truck is restricted to "crawl" speed.

Diagnosis & fix steps

DEF Pressure Too Low. LOGIC: The aftertreatment system cannot build the required 5 bar (approx 72 psi) of DEF pressure. ACTION: Check for frozen DEF lines in winter or a clogged DEF pump filter.

Red Seal field insights

Pro-Tip: If the pump is humming but there's no pressure, the "inlet strainer" at the bottom of the DEF tank is likely crystallized. Wash it with hot distilled water to dissolve the urea crystals.

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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