Liebherr Fault Code

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P204C-00

DEF Derate. Check Engine light on; AdBlue/DEF pressure fails to build; machine may limit RPM/torque.

System

Aftertreatment (SCR)

Symptom

DEF Derate. Check Engine light on; AdBlue/DEF pressure fails to build; machine may limit RPM/torque.

Diagnosis & fix steps

Reductant (DEF) Pressure Sensor Circuit Low. LOGIC: The SCR control module detects a voltage signal from the DEF pressure sensor that is below the minimum threshold (typically < 0.25V). ACTION: Check the DEF pump harness for chafing. Verify 5V reference at the sensor.

Red Seal field insights

Pro-Tip: On Liebherr rigs, the DEF lines are heated. P204C-00 often occurs in cold weather if the DEF has frozen in the pump head and "cracked" the internal ceramic pressure sensor. Red Seal Fix: Before replacing the pump, check the "Return Valve" (Purge Valve). If it's stuck open, the system can't build pressure, and the sensor correctly reports "Low," which the computer sometimes misinterprets as a circuit fault.

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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