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| Illustration 1 | g03414466 |
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Diesel Exhaust Fluid (DEF) dosing control cabinet components Valves are shown in a static state (1) Dosing control cabinet (2) DEF line to injector at CEM (3) Air line to injector at CEM (4) Compressed air source (customer supplied) (5) DEF main tank return line (6) DEF source (main tank) (7) DEF pressure sensor (8) Air assist pressure sensor (9) Air pressure regulator (10) Air assist valve (solenoid) (11) DEF main tank return valve (solenoid) (12) DEF main tank return valve (pneumatic) (13) DEF pump | |
The following table is for components located in the dosing control cabinet.
| Solenoid Valves | Pneumatic Valves | ||
|---|---|---|---|
| System State | Air Assist | DEF Main
Tank Return |
DEF Main
Tank Return |
| Dormant (sleep mode) | Closed
Static state |
Open
Static state |
Open
Static state |
| Protect mode against cold (defreeze) | Closed | Open | Open |
| Preparing dosing readiness
Step 1 |
Open | Open | Closed |
| Preparing dosing readiness
Step 2 |
Open | Closed | Open |
| Preparing dosing readiness
Step 3 |
Closed | Closed | Open |
| Preparing dosing readiness
Step 4 |
Open | Open | Closed |
| Normal dosing operation | Open | Open | Closed |
| Dormant (sleep mode) | Closed | Open | Closed |
| Shutoff ( wait for after-run) | Open | Closed | Open |
For the information contained in Troubleshooting, "Warning Operation", observe the following definitions.
Open - Flow of air or flow of DEF
Closed - No flow of air or no flow of DEF
The SCR dosing system is waiting for engine or aftertreatment conditions to be met. The dosing system will enter dormant sleep mode when any of the following are true:
- The engine is not running.
- Not all aftertreatment electronics are ready.
- The dosing control is not requesting DEF flow.
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 DEF heating system uses a combination of heaters. Some heaters are sized to thaw DEF. Some heaters are sized to prevent freezing only of DEF . Freezing will be prevented down to
When powered, the system will maintain DEF temperature to a minimum of
The following are monitored by sensors:
- DEF tank temperature
- DEF manifold temperature
- Ambient temperature of the dosing cabinet
DEF system components that are heated include the following:
- DEF tank
- DEF pump
- DEF manifold
- DEF lines
The customer must provide power to the heater when the engine is shut down, and there is a freeze potential. If power is not provided, the customer is required to drain the DEF tank.
The DEF pump does not require draining when there is a freeze potential.
DEF is allowed to freeze in the pump. The heater can thaw frozen DEF within 70 minutes of engine startup.
The DEF manifold does not require draining when there is a freeze potential.
DEF is allowed to freeze in the manifold. The heater can thaw frozen DEF within 70 minutes of engine startup.
DEF line heaters can prevent lines from freezing during engine operation.
DEF lines are purged with air when engine shuts down.
The dosing system checks the operation of the air 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.
The air assist valve (solenoid) is energized causing the valve to open. The resulting air pressure is measured at the DEF pressure sensor.
This action is taken to check for the following conditions:
- Blockage in the DEF lines
- Stuck DEF main tank return valves
- All air lines and DEF lines are present and properly connected
The DEF return valve (solenoid) is energized causing the valve to close. This action causes the DEF return valve (pneumatic) to open and the expected result is a drop in pressure at the DEF pressure sensor.
If a pressure drop does not result, the DEF return valve may be stuck or a line may be plugged.
If a pressure drop does not result, a code will be set and the system will return to the dormant state.
The air assist valve (solenoid) is de-energized causing the valve to close. This action reduces the back pressure on the DEF dosing pump.
The DEF dosing pump is commanded on by the aftertreatment ECM and circulates DEF back into the DEF main tank. This action primes the DEF dosing pump.
The DEF return valve (solenoid) is de-energized causing the valve to open.
This action causes the DEF return valve (pneumatic) to close resulting in the pump priming DEF to the injector.
Once DEF pressure indicates a complete system prime, the SCR dosing system will move on to normal dosing operation.
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, a code will be set and the system will return to the dormant state.
If the exhaust temperature has reached
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 main tank as long as 24V is still provided to the Dosing Cabinet.
Note: If the system is stopped by emergency stop, the shutoff state will fail to purge from the injector to the DEF main tank completely. The emergency stop will remove the 24V supply from the dosing cabinet.