Note: The term Diesel Exhaust Fluid (DEF) and the word reagent are used interchangeably in some code descriptions and labels.
| Event Code | ||
|---|---|---|
| Code and Description | Conditions which Generate this Code | System Response |
| E931 (1)
Low Aftertreatment #1 SCR Dosing Reagent Pressure |
The DEF pressure is below the trip point for the programmed delay time. | The code is logged.
Dosing is disabled until the pressure is correct. |
Note: Use Cat ET to verify any suspected code. Determine what codes are present. Evaluate all codes for possible interaction. Refer toTroubleshooting, "Diagnostic Trouble Codes" and Troubleshooting, "Event Codes" for direction.
- Leak between the DEF pump and DEF injector
- Supply air pressure is low
- Dosing air assist pressure is low
- DEF main tank is empty
- DEF main tank is frozen
- DEF return valve (pneumatic) is stuck open
- Low DEF pump flow rate
Note: If you also have a 4335-17 Aftertreatment 1 SCR Dosing Air Assist Absolute Pressure : Low - least severe (1) then troubleshoot the 4335-17 code first.
Note: A system health test is run during the "Prepairing Dosing Readiness" system state. The air assist valve (solenoid) is opened creating a pressure in the DEF line. A pressure range is expected to be sensed by the DEF pressure sensor. The DEF pressure is also monitored during the "Normal Dosing Operation" system state. The expected pressure during dosing will vary with the desired DEF flow rate.
Leak Between DEF Pump and DEF Injector
Inspect the DEF line and the DEF manifold. Ensure that the DEF line is connected and leak free.
Check the pressure gauge for the air supply to the dosing cabinet.
The cabinet requires a regulated air pressure range of
Ensure that all air lines are connected and leak free.
Dosing Air Assist Pressure is Low
Note: Attempting to adjust the regulator will destroy the regulator. The only service option is to replace the regulator.
There may be a problem with the air pressure regulator in the dosing cabinet.
Monitor the status for "Aftertreatment #1 SCR Dosing Air Assist Absolute Pressure" on Cat ET. This pressure is measured at the output of the air assist valve (solenoid).
Activate the "Aftertreatment #1 SCR Dosing Air Assist Valve Command Override" and record the pressure. The pressure must be in the range of
Replace the regulator if the pressure is out of range.
Determine if the DEF main tank is empty.
If the tank is empty Refer to Troubleshooting, "DEF Tank Level Is Low "
Ensure that the DEF main tank is not frozen.
The DEF main tank temperature can be viewed through Cat ET or a display.
If the DEF is frozen, Refer to Troubleshooting, "Relay - Test" in order to troubleshoot the heater circuit.
Check Cat ET for either of the following:
- 3363-5 Catalyst Tank Heater : Current Below Normal
- 3363-6 Catalyst Tank Heater : Current Above Normal
DEF Return Valve (pneumatic) is Stuck Open
Activate the "Aftertreatment #1 SCR Dosing Air Assist Valve Command Override" to ON in order to open the air assist valve (solenoid).
That action should cause the DEF return valve (pneumatic) to be closed.
Monitor the status for "Aftertreatment #1 SCR Dosing Reagent Absolute Pressure" on Cat ET.
The pressure must be in the range of
Check the DEF manifold for an air pressure leak. An air pressure leak will not allow the DEF return valve (pneumatic) to actuate closed.
Ensure that the DEF return valve (solenoid) is in the normally open state (static state).
If the DEF return valve (pneumatic) is suspected, remove the valve from the manifold leaving the air line attached.
Override the air assist valve (solenoid) again as described before and look for the DEF return valve (pneumatic) to actuate.
Note: A breaker located in the dosing cabinet, controls AC power to the pump.
Determine if the DEF dosing pump is powered. Measure the voltage supply to the DEF dosing pump. Look for any fluctuations in supply power to the DEF dosing pump. The supply voltage to the DEF dosing pump should measure 120 VAC.
Test the DEF dosing pump for a sufficient flow rate. Refer to Testing and Adjusting, "Aftertreatment SCR System Dosing Test"