CAP ASSEM. 6N2958 - Caterpillar

System check
During normal engine operation the ECM will elevate the fuel pressure to the injectors. This check will be at scheduled intervals of approximately 100 hours depending on the duty cycle of the engine. The check will be carried out automatically without the need of any input from the operator.During the time of elevated fuel pressure, the operator may notice a change in the tone of the engine. The ECM will operate the check at low idle for approximately 5 minutes.Aftertreatment
The exhaust gases pass through the DOC and then the mixer where the gases are mixed with the injected urea. The mixture then enters the SCR catalyst. Here the NOx in the exhaust reacts with the ammonia from the injected urea to split the gases into nitrogen and oxygen constituents. The SCR catalyst includes an ammonia oxidation section to clean up any remaining ammonia before the gases exit the system.For the aftertreatment system to operate correctly the operator must ensure an adequate diesel exhaust fluid supply. The aftertreatment system must operate correctly in order for the engine to be emissions-compliant.Elevated Idle for Aftertreatment
In some applications the engine low idle RPM will automatically increase in order to lower the rate of hydrocarbon build-up within the SCR. The elevated idle is controlled by the engine ECM. The software within the ECM will calculate the build-up of hydrocarbon and will increase idle RPM.The hydrocarbon build-up occurs when the engine is left to idle for a long period. Operating the engine in normal load conditions will remove the hydrocarbon from the SCR.Constant speed engines and engines with an idle speed at or above 1100 RPM will not require the increase in the idle speed.In some application the ECM software may be configured in order to protect the aftertreatment system from high hydrocarbons build up. This protection will shut down the engine.