Diesel Emissions Fluid Control Module: Description and Operation

Diesel Exhaust Fluid (DEF) Control Module Description

Diesel Exhaust Fluid (DEF) Control Module Service Precautions






The DEF control module is designed to withstand normal current draws associated with vehicle operation. Avoid overloading any circuit. When testing for opens and shorts, do not ground or apply voltage to any of the ECM circuits unless instructed to do so. In some cases, these circuits should only be tested using a DMM. The DEF control module should remain connected to the DEF control module harness.

The DEF control module is located behind the front bumper via mounting bracket. The DEF control module mainly controls the following.
- The heater control
- The start-up control
- The dew point control
- The dosing control
- The NH3 storage control
- The DPF control
- The after run control
- On-board diagnostics

The DEF control module constantly observes the information from various sensors. The DEF control module controls the systems that affect vehicle performance. The DEF control module performs the diagnostic function of the system. The DEF control module can recognize operational problems, alert the driver through the malfunction indicator lamp (MIL), and store diagnostic trouble codes (DTCs). DTCs identify the system faults to aid the technician in making repairs.

DEF Control Module Input & Output






Malfunction Indicator Lamp (MIL) Operation
The MIL is located in the instrument panel cluster. The MIL will display the following symbols when commanded ON:






The MIL indicates that an emission related fault (Type A or B) has occurred and vehicle service is required. The following is a list of the modes of operation for the MIL:
- The MIL illuminates when the ignition switch is turned ON, with the engine OFF. This is a lamp test to ensure the MIL is able to illuminate.
- The MIL turns OFF after the engine is started if a diagnostic fault is not present.
- The MIL remains illuminated after the engine is started if the DEF control module detects a fault. A DTC is stored any time the DEF control module illuminates the MIL due to the following conditions fault.
- Malfunction of the engine or exhaust electronic control system.
- DEF level is too low or empty.
- DEF tank is refilled with a fluid (such as water or low-concentrated the DEF, etc) other than the DEF.

Service Vehicle Soon (SVS) Lamp Operation
The service vehicle soon (SVS) lamp is located in the instrument panel cluster. The SVS lamp will display the following symbol when commanded ON:






The SVS lamp indicates that an non-emission related fault (Type C DTC) has occurred and vehicle service required. The following is a list of the modes of operation for the SVS lamp:
- The SVS lamp illuminates when the ignition switch is turned ON, with the engine OFF. This is a lamp test to ensure the SVS lamp is able to illuminate.
- The SVS lamp turns OFF after the engine is started if a diagnostic fault is not present.
- The SVS lamp remains illuminated after the engine is started if the DEF control module detects a fault. A DTC is stored any time the DEF control module illuminates the SVS lamp due to a non-emission related fault.

Reduced Engine Power Indicator Lamp Operation
The reduced engine power indicator lamp is located in the instrument panel cluster. The reduced engine power indicator lamp will display the following symbols when commanded ON:






The reduced engine power indicator lamp indicates that the following conditions fault has occurred and vehicle service is required.
- Malfunction of the engine or exhaust electronic control system.
- DEF level is too low or empty.
- DEF tank is refilled with a fluid (such as water or low-concentrated the DEF, etc) other than the DEF.

The following is a list of the modes of operation for the reduced engine power indicator lamp:
- The reduced engine power indicator lamp illuminates when the ignition switch is turned ON, with the engine OFF. This is a lamp test to ensure the reduced engine power indicator lamp is able to illuminate.
- The reduced engine power indicator lamp turns OFF after the engine is started if a diagnostic fault is not present.
- The reduced engine power indicator lamp remains illuminated after the engine is started if the DEF control module detects a fault. A DTC is stored any time the DEF control module illuminates the reduced engine power indicator lamp due to the following conditions fault.
- Malfunction of the engine or exhaust electronic control system.

Diesel Exhaust Fluid (DEF) Indicator Lamp Operation
Diesel exhaust fluid (DEF) indicator lamp is located in the instrument panel cluster. The diesel exhaust fluid (DEF) indicator lamp will display the following symbols when commanded ON:






The diesel exhaust fluid (DEF) indicator lamp indicates that the following conditions fault has occurred and vehicle service is required.
- Malfunction of the SCR control system.
- DEF level is too low or empty.
- DEF tank is refilled with a fluid (such as water or low-concentrated the DEF, etc.) other than the DEF.

The following is a list of the modes of operation for the diesel exhaust fluid (DEF) indicator lamp:
- The diesel exhaust fluid (DEF) indicator lamp illuminates when the ignition switch is turned ON, with the engine OFF. This is a lamp test to ensure the diesel exhaust fluid (DEF) indicator lamp is able to illuminate.
- The diesel exhaust fluid (DEF) indicator lamp turns OFF after the engine is started if a diagnostic fault is not present.
- The diesel exhaust fluid (DEF) indicator lamp remains illuminated after the engine is started if the DEF control module detects a fault.

A DTC is stored any time the DEF control module illuminates the diesel exhaust fluid (DEF) indicator lamp due to the following conditions fault.
- Malfunction of the SCR control system.
- DEF level is too low or empty.
- DEF tank is refilled with a fluid (such as water or low-concentrated the DEF, etc.) other than the DEF