Cummins ISX15 CM2250 (2010-12) Fault Code: 1678 PID: SPN: 3031 FMI: 3 Aftertreatment Diesel Exhaust Fluid Tank Temperature Sensor- Voltage Above Normal or Shorted to High Source

Circuit Description
The aftertreatment diesel exhaust fluid temperature sensor is used to monitor the temperature of the aftertreatment diesel exhaust fluid inside the diesel exhaust fluid tank. The diesel exhaust fluid controller monitors the voltage on the signal pin, converts this to a temperature value, and communicates this value to the engine ECM.

Component Location
The aftertreatment diesel exhaust fluid temperature sensor is located in the diesel exhaust fluid tank. Location of the tank and temperature sensor is OEM dependent. Refer to the OEM service manual.

Conditions for Running the Diagnostics
This diagnostic runs continuously when the keyswitch is in the ON position.

Conditions for Setting the Fault Codes
The diesel exhaust fluid controller detects that the diesel exhaust fluid tank temperature signal voltage is higher than 4.7-VDC for more than 1 second.

Action Taken When the Fault Code is Active
The ECM illuminates the amber CHECK ENGINE light and/or the Malfunction Indicator Lamp (MIL) immediately when the diagnostic runs and fails.
Engine torque will be reduced if the engine is operated for a limited period of time with the fault code active.
Engine torque will be severely reduced and vehicle speed will be limited to 8 km [5 mi] per hour after extended engine operation with the fault code active.
Conditions for Clearing the Fault Code
To validate the repair, perform a key cycle. Then start the engine and let it idle for 1 minute.
The fault code status displayed by INSITE? electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
The ECM will turn off the amber CHECK ENGINE lamp after the diagnostic runs and passes.
For OBD engines, the ECM will turn off the MIL after 3 consecutive trips where the diagnostic runs and passes.
The ?Reset All Faults? command in INSITE? electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop Talk
Possible causes of this fault code include:

Open return circuit in the harness, connectors, or sensor
Open signal circuit or shorted to a voltage source.
The type of diesel exhaust fluid tank temperature and level sensor used can vary depending on the vehicle OEM. As a result, the physical and/or electrical sensor configuration may vary slightly from what is shown in the troubleshooting and wiring diagram information.

Reference the appropriate OEM wiring diagram when troubleshooting circuits that utilize wiring supplied by the OEM.

For intermittent power supply and datalink communication issues with Aftertreatment Components, it is highly recommended that the OEM Power Distribution Center fuses and relays be thoroughly checked for loose, missing or intermittent connections.

Possible Cause:
1) Aftertreatment DEF controller failure
2) ECM calibration