Cummins X15 CM2450 X124B (2018 & Newer) Fault Code: 3543 PID: SID 115 SPN: 4094 FMI: 31 Nox Limits Exceeded Due to Insufficient Reagent Quality- Condition Exists

Circuit Description
The engine control module (ECM) monitors the NOx concentration in the engine’s exhaust gases using an aftertreatment intake NOx sensor and an aftertreatment outlet NOx sensor. By comparing these two values, the ECM is able to determine the conversion efficiency of the SCR catalyst and dosing system.

Component Location
The SCR catalyst is located in the vehicle’s exhaust system, after the diesel particulate filter and decomposition tube.

Conditions for Running the Diagnostics
This diagnostic has to meet specific engine and aftertreatment conditions to run and complete.

Conditions for Setting the Fault Codes
The Engine Control Module (ECM) detected the NOx conversion across the SCR catalyst was less than expected, and the diesel exhaust fluid tank has recently been refilled.

Action Taken When the Fault Code is Active
The ECM illuminates the amber CHECK ENGINE lamp and/or the Malfunction Indicator Lamp (MIL) immediately when the diagnostic runs and fails.
Engine torque will be reduced if the engine is operated for an extended period of time with this fault active.
Conditions for Clearing the Fault Code
It is necessary to use the “Reset All Faults” command in INSITE™ electronic service tool to clear this fault and extinguish the amber CHECK ENGINE lamp and/or Malfunction Indicator Lamp (MIL).

Shop Talk
Troubleshoot all other active NOx sensor and SCR dosing system related fault codes before this fault.

Possible causes of this fault include:

Malfunctioning diesel exhaust fluid dosing system
Exhaust system leaks
Malfunctioning SCR catalyst
Degraded, diluted, or incorrect diesel exhaust fluid
Diesel exhaust fluid deposits in the decomposition tube.

Possible Cause:
1) DEF tank
2) ECM calibration