RAM Fault Code

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P20EE

"SCR Efficiency Below Threshold"; Check engine light; Potential DEF derate timer.

System

Not specified

Symptom

"SCR Efficiency Below Threshold"; Check engine light; Potential DEF derate timer.

Diagnosis & fix steps

SCR NOx Catalyst Efficiency Below Threshold. LOGIC: The ECM compares the Inlet NOx sensor to the Outlet NOx sensor. If the reduction in NOx isn't high enough, it triggers the code. ACTION: 1. Check DEF quality with a refractometer (32.5%). 2. Inspect DEF injector for "crystal" buildup. 3. Check for exhaust leaks before the SCR. FIX: Replace DEF Injector; clean SCR catalyst; or replace Outlet NOx sensor.

Red Seal field insights

Most P20EE codes are caused by a crystallized DEF injector. Before replacing sensors, pull the injector and soak the tip in hot distilled water to dissolve the white buildup.

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.

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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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