CM850 Electronic Control System – FAULT CODE 1682

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Overview

Aftertreatment Control System Circuit SMALL | MEDIUM | LARGE

Circuit Description

For an air-assisted SCR aftertreatment system, the aftertreatment diesel exhaust fluid (Urea) dosing unit requires air pressure from the OEM air tanks. The diesel exhaust fluid dosing unit precisely measures the amount of diesel exhaust fluid to be injected into the aftertreatment system. The diesel exhaust fluid dosing unit has three primary cycles. A priming cycle at initial engine start makes sure that diesel exhaust fluid is available at the diesel exhaust fluid dosing unit. During the dosing cycle, the diesel exhaust fluid is being delivered to the aftertreatment nozzle. A purge cycle occurs when the engine is turned off. The purge cycle makes sure that all the diesel exhaust fluid is removed from the diesel exhaust fluid line and aftertreatment nozzle.

Component Location

The aftertreatment diesel exhaust fluid dosing unit location is OEM dependent. Refer to the OEM service manual for more information.

Conditions for Running the Diagnostics

This diagnostic consists of multiple parts, which run on engine “Run”. This can take up to 12 minutes. If the Doser Override Test passed after the repair, the repair is considered to be complete.

Conditions for Setting the Fault Codes

The aftertreatment diesel exhaust fluid dosing unit is not able to provide the correct dosing rate to the aftertreatment nozzle.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light and/or the MIL (malfunction indicator lamp) immediately when the diagnostic runs and fails.
• An engine torque derate will be activated after 50 hours of engine operation with the fault code active, if the engine has a NOx sensor fitted.
• Diesel exhaust fluid injection into the SCR aftertreatment system is disabled. The Dosing Unit status in INSITE™ electronic service tool will be OFF.

Conditions for Clearing the Fault Code

• This fault code can not be cleared with INSITE™ electronic service tool while it is active.
• To validate the repair, it is necessary to use INSITE™ electronic service tool to perform the Diesel Exhaust Fluid Doser Pump Override Test. Refer to Procedure 019-440 in Section 19.
• Make sure the diesel exhaust fluid dosing unit is able to successfully cycle through all phases (priming, dosing, and purging) and that diesel exhaust fluid flows evenly from the aftertreatment nozzle.
• The ECM will turn off the amber CHECK ENGINE light and/or MIL immediately after the diagnostic runs and passes (engines with NOx sensors only).
• Use INSITE™ electronic service tool to verify that the fault code is inactive.
• The inactive fault code will be cleared from memory automatically after the completion of 9600 hours of operation without a reoccurrence.

Shop Talk

The diesel exhaust fluid dosing unit process consists of three phases, which occur in the following sequence: priming, dosing, and purging.

Priming:

• The diesel exhaust fluid dosing unit will attempt to prime every 30 seconds for 20 attempts. The attempts can be counted by listening for the air solenoid to click every 30 seconds.
• The diesel exhaust fluid dosing unit can take up to 12 minutes to complete the priming cycle before a fault code will become active.
• During priming, the diesel exhaust fluid dosing unit will pump diesel exhaust fluid through the supply and return lines, and back to the tank.
• Under most conditions, the system will prime within 3 or 4 attempts.
• If priming is not successful, the diesel exhaust fluid dosing unit will be disabled and Fault Code 1682 will be activated.

Dosing:

• Immediately after successful priming, the system will go into the dosing mode, the solenoid will stop clicking, and a constant flow of air will flow through the aftertreatment nozzle, which helps transport the diesel fluid and keeps the aftertreatment nozzle clear.
• The air flow will remain constant until the system reaches all dosing conditions before diesel exhaust fluid is delivered to the aftertreatment system (catalyst temperature greater than 200°C [392°F], engine speed and load conditions met, etc.).

Purging:

• After the engine is stopped and the keyswitch is turned off, the dosing unit enters the purging cycle, which clears any diesel exhaust fluid left in the line and the aftertreatment nozzle after operation.
• Purging consists of flowing compressed air through the aftertreatment nozzle and diesel exhaust fluid line for 30 seconds.
• If the full purge time is not completed, it is possible to leave diesel exhaust fluid in the line, leading to a buildup of hard urea crystals, resulting in a blocked diesel exhaust fluid line or aftertreatment nozzle.
• If the vehicle is equipped with a battery isolation switch, it should have a built-in delay device to prevent power down of the dosing unit until the purge sequence is completed.
• Incomplete purge events are recorded by the ECM and by increments at the next keyswitch ON event.
• Incomplete purge counts can be viewed using the Data Monitor/Logger menu in the aftertreatment section of INSITE™ electronic service tool.

Fault Code 1682 is triggered by the following external failure modes:

• Low aftertreatment diesel exhaust fluid level in the diesel exhaust fluid tank
• Low air pressure is detected at the dosing control unit
• Air pressure is cycling below the minimum limit required by the dosing control unit
• Blocked or restricted aftertreatment nozzle
• Blocked or restricted/frozen diesel exhaust fluid lines
• Plugged or restricted inline air filter.
• By the operation of the SCR aftertreatment system in environments where the ambient temperature falls below -11 degrees C, without suitable line and tank heating protection.
• This can lead to the freezing of the dosing control unit (DCU), and can cause permanent internal damage to the DCU.

Fault Code 1682 is triggered by the following internal diesel exhaust fluid dosing unit failure modes:

• Diesel exhaust fluid dosing unit fails to initialize on keyswitch ON (fault code will be active immediately after keyswitch ON)
• Buildup of urea crystals in the dosing unit restricts air flow to the aftertreatment nozzle, and possibly leads to buildups and restrictions in the aftertreatment nozzle itself. This results in low/no air flow to the nozzle
• Internal pressure sensor malfunction – pump does not prime and diesel exhaust fluid is injected as the air solenoid operates during priming. Fault Code 1682 will become active after 12 minutes of consecutive priming attempts
• Internal poppet valve malfunction, causing priming to not occur. This will cause diesel exhaust fluid to flow continuously during priming (fault code will be active after 12 minutes of failed priming attempts)
• Contamination in the dosing unit inlet check valve from an external source, such as the diesel exhaust fluid line or tank
• Diesel exhaust fluid dosing unit drawing in air through loose or damaged lines or connectors.

Refer to Troubleshooting Fault Code t05-1682