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| Illustration 1 | g06306533 |
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(1) Air source
(2) Air regulator (3) Air assist solenoid valve (4) Nozzle (5) Air pressure sensor (6) DEF line/manifold purge solenoid (7) DEF pressure sensor (8) DEF pump (9) DEF manifold (10) DEF pump purge solenoid (11) 40 micron strainer (12) 40 micron OEM DEF filter (12) DEF tank (13) Air manifold | |
The DEF pump is located in the dosing cabinet. The DEF pump is powered by a 230 VAC power source.
The Electronic Control Module (ECM) controls the DEF pump by sending a Pulse Width Modulated (PWM) signal to the pump.
The DEF pump is a fixed displacement pump. The higher the duty cycle of the PWM signal, the more DEF is dosed into the exhaust stream.
The air manifold is where all the air connections to the dosing cabinet are made.
The air manifold contains internal passages for the air and contains the air assist solenoid valve and the air pressure regulator.
The DEF manifold is where all the DEF connections to the dosing cabinet are made.
The DEF manifold contains internal passages for the DEF and contains the solenoids required for operation of the DEF manifold portion of the dosing system.
The DEF lines are connected to the dosing cabinet.
The DEF supply line is routed from the remote customer tank to the DEF inlet on the dosing cabinet.
The DEF injector supply line is routed from the outlet of the dosing cabinet to the DEF injector on the Clean Emissions Module (CEM).
Both of these lines are supplied by the customer.
Protect Mode Against Cold (defreeze)
The system will enter protect mode against cold for either of the following:
- DEF manifold temperature drops below
−5° C (23° F) - DEF tank temperature drops below
−10° C (14° F)
Temperature sensors are monitored to indicate if there is a freeze potential for the DEF. Heaters are utilized to prevent the freezing of DEF.
Upon completion of the protect mode against cold, the process will continue on to preparing dosing readiness.
The Selective Catalyst Reduction (SCR) dosing system checks the operations of the air assist valve, DEF control valves, and DEF dosing pump.
The system will annunciate a fault code for any unexpected voltage, current, or pressure values.
The system will continue to cycle the valves until all indications determine the system is ready to dose DEF.
Step 1 Preparing Dosing Readiness
The air assist valve is energized causing the valve to open. The resulting air pressure is measured at the DEF pressure sensor. The pump purge solenoid valve is de-energized causing the valve to open. The resulting air pressure is measured at the DEF pressure sensor to confirm functionality of the valve.
This action is taken to check for the following conditions:
- Blockage in the DEF lines or air lines
- Leak in DEF lines or air lines
- Stuck open DEF line/manifold purge solenoid valve
- All air lines and DEF lines are present and properly connected
- Plugged injector/lance
Step 2 Preparing Dosing Readiness
The DEF line/manifold purge solenoid valve is de-energized resulting in the valve to open. The expected result is a drop in pressure at the DEF pressure sensor. This will confirm the functionality of the DEF line/manifold purge solenoid valve, DEF line continuity, and the DEF nozzle is not plugged. If a pressure drop does not occur, the valve may be stuck or the tank vent is plugged. A code will be set and the system will return to the dormant state.
The DEF Line/manifold purge solenoid valve is de-energized opening the valve and the DEF dosing pump is commanded on by the SCR system ECM and circulates DEF back into the DEF tank. This action primes the DEF dosing pump.
The DEF line/manifold purge solenoid valve is energized causing the valve to close. This results in the pump priming DEF to the injector.
The air assist valve is energized causing the valve to open. Once DEF pressure indicates a complete system prime, the SCR dosing system will move on to normal dosing operation.
Note: If the system fails to build sufficient pressure in Step 4, the system will return to Step 3 multiple times in an attempt to build pressure. If the system still cannot build pressure, an event code will be set and the system will return to the dormant state.
If the exhaust temperature has reached
Permanent Purge (SHUTOFF): When the system is shutdown it will remove DEF from the nozzle, pump, manifold, and lines back to the DEF tank. The system will continue to flow air through the nozzle until the "Aftertreatment #1 SCR Catalyst Intake Gas Temperature" is less than
When any dosing component that is required to maintain proper NOx reduction fails, a code will be set. If the condition goes away, the dosing process will resume. The dosing system will automatically purge from the injector to the DEF tank as long as 24V is still provided to the dosing control cabinet.
Permanent Purge (System Issue): If there is an issue detected within the dosing pump or pump command relay the system will enter permanent purge. The air valve will be open and return valve will be open, causing the DEF to return to the DEF tank.
Note: Once the condition causing this state is healed, the power to the dosing cabinet will have to be power cycled to reset the system and to heal the system.