94002-12490-0S Honda NUT, HEX. (12MM)

System Block Diagram
Illustration 1 g06171267
(1) Turbocharger
(2) Diesel Exhaust Fluid (DEF) injectors
(3) Clean Emissions Module (CEM)
(4) Mixer
(5) Selective Catalyst Reduction (SCR)
(6) Exhaust Out
(7) Pump Electronic Tank Unit (PETU)
(8) Aftertreatment #1 DEF Pump #1
(9) Aftertreatment #1 DEF Pump #2
(10) Aftertreatment #2 DEF Pump #1
(11) Aftertreatment #2 DEF Pump #2
(12) DEF Tank
(13) Heating Element
(14) Coolant to and from the DEF injectors
(15) Electrical connection
(16) Coolant to and from the PETU
(17) DEF fluid to DEF injectors
(18) Ground fill system
(19) CEM inlet
(20) BellowsDiesel Exhaust Fluid (DEF)
Note: The tool to measure the DEF concentration is the 431-7087 Tool Gp (Refractometer (DEF). Refer to Testing and Adjusting, “Diesel Exhaust Fluid Quality - Test” for additional information.Selective Catalyst Reduction (SCR) refers to a method of treating engine exhaust to reduce the undesired oxides of nitrogen compounds NOx. SCR uses a catalyst which promotes a desired chemical reaction over other possible chemical reactions. The catalyst remains unchanged. Ammonia (NH3) is mixed into the exhaust, and reacts with the NOx in the presence of the catalyst to form harmless compounds (water and nitrogen). In this system, urea ((NH2)2CO) is injected into the exhaust, which quickly decomposes into ammonia under the heated conditions. Urea is used because urea is inexpensive, and does not need the special handling that ammonia requires.DEF is an aqueous urea solution (urea salt dissolved in water).A 32.5 percent or 40 percent (by weight) solution of DEF is required for the system.A 32.5 percent concentration has the lowest freezing point possible, −11 °C (11 °F), for this solution.A 32.5 percent concentration of urea keeps a constant concentration through freezing and thawing.DEF must be stored below 50 °C (122 °F) to delay decomposition.Use only DEF that meets quality properties per ISO 22241-1. Using DEF that does not meet ISO 22241-1 can result in clogging of the injection nozzle.DEF is a non-toxic source of ammonia.DEF is corrosive. Do not store DEF in a tank or use supply lines that are made of the following materials: aluminum, brass, and steel. Use only corrosion resistant materials such as PVC or stainless steel. Any O-rings must be Ethylene Propylene Diene Monomer (EPDM).Clean Emissions Module (CEM)
Illustration 2 g06309582
(1) Exhaust in
(2) DEF injector
(3) Mixers
(4) Diffuser plate
(5) Catalyst brick
(6) Inlet NOx sensor
(7) Pressure sensor
(8) Coolant shunt tank
(9) Exhaust out
(10) Outlet NOx sensor
Illustration 3 g06309620
(2) DEF injector
(6) Inlet NOx sensor
(7) Pressure sensor
(8) Coolant shunt tank
(11) Inlet temperatureThe exhaust gas exits the engine and enters the mixing tube, where the DEF is injected into the exhaust stream.The DEF decomposes into ammonia and carbon dioxide.The mixture of exhaust and ammonia travels through the SCR.The ammonia reacts with the NOx in the exhaust stream at the SCR catalyst to produce water vapor and nitrogen.Pump Electronic Tank Unit (PETU)
Illustration 4 g06521071
(1) DCU
(2) Coolant diverter valve
(3) Manual fill
(4) DEF pump
(5) Drain plug
(6) DEF header
(7) DEF header heating element
(8) Back flow valve
Illustration 5 g06521089
(9) Ground level fill valve
(10) Ground level fill hoseCEM Identification Number Module
The identification number module outputs a 10 character alphanumeric serial number for the CEM to the SCR system ECM.The SCR system ECM transmits this data to the engine ECM over the local CAN data link.The engine ECM compares the first 3 letters of the serial number (the prefix) to a value programmed into the engine software.Sensors (CEM)
NOx Sensors
The NOx sensor communicates to the SCR system ECM over the CAN data link. The sensor has built-in diagnostics to indicate sensor failure modes.The SCR system ECM controls the power supply to the NOx sensors.Aftertreatment #1 Intake NOx Sensor
The aftertreatment #1 intake NOx sensor is monitored to control the DEF dosing rate based on engine out emissions levels.Aftertreatment #2 Intake NOx Sensor
The aftertreatment #2 intake NOx sensor is monitored to control the DEF dosing rate based on engine out emissions levels.Aftertreatment #1 Outlet NOx Sensor
The aftertreatment #1 outlet NOx sensor is monitored to control the DEF dosing rate based on catalyst out emissions. The SCR system ECM monitors the sensor to calculate the necessary DEF flow rate to meet emission targets.Aftertreatment #2 Outlet NOx Sensor
The aftertreatment #2 outlet NOx sensor is monitored to control the DEF dosing rate based on catalyst out emissions. The SCR system ECM monitors the sensor to calculate the necessary DEF flow rate to meet emission targets.Temperature Sensors
Aftertreatment #1 SCR Catalyst Intake Gas Temperature Sensor
The aftertreatment #1 SCR catalyst intake gas temperature sensor is monitored for dosing control and system protection.The temperature indicates the capability of the SCR system ECM to calculate the DEF dosing rates. The temperature is monitored to indicate temperatures that are too low or too high.