Cummins ISB CM850 (2003-06) Fault Code: 1689 PID: 251 SPN: 251 FMI: 12 Real-Time Clock Power Interrupt – Data Erratic, Intermittent or Incorrect. The Real-Time clock power has been interrupted.

Posted by PerDiezel Solutions on January 18, 2026

This fault indicates that the real-time clock in the ECM lost power. Possible causes for this fault are weak or failed real-time clock battery, failed wiring or connectors between the battery and ECM, or the engine is not equipped with a real-time clock battery and the vehicle battery power to the ECM is lost.

NOTE:If the Real Time Clock is supplied by the OEM via a CAN BUS and a battery backup is not used, then refer to the OEM wiring diagram. If this is the case, then` check INSITE? electronic service tool, ?Advanced ECM Data – Real Time Clock Settings.? If the OEM supplies a Real Time Clock signal, then the address must be set according to the OEM wiring or the fault code will become active.

On-Board Diagnostics (OBD) Information (Euro 4 Certified Engines):

1)The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2)The ECM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. The malfunction indicator lamp and fault code can also be cleared using the INSITE? electronic service tool.
3)The fault code will be cleared from memory after 40 consecutive drive cycles where the diagnostic runs and passes.

On-Board Diagnostics (OBD) Information (Euro 4 Stage 1+ Certified Engines):

1)The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2)An engine torque derate will be activated after 50 hours of engine operation with the fault code active.
3)The ECM turns OFF the malfunction indicator lamp (MIL) after 1 ignition cycle that the diagnostic runs and does not fail. The malfunction indicator lamp and fault code can also be cleared using the INSITE? electronic service tool.
4)The fault code will be cleared from memory after 400 days or 9600 hours of engine operation.

Possible repairs:

1)Flush the dirt, debris, or moisture from the connector pins. Use electronic cleaner, Part Number 3824510.
2)Install the appropriate connector seal if it is damaged or missing.
3)Repair the engine harness.
4)Repair or replace the real-time clock battery.

Cummins ISB CM850 (2003-06) Fault Code: 1687 PID: SPN: 3050 FMI: 0 Catalyst Over Temperature – Data Valid but Above Normal Operational Range – Most Severe Level. Very high temperatures have been detected in the aftertreatment system.

Cummins ISB CM850 (2003-06) Fault Code: 1684 PID: SPN: 3363 FMI: 4 Catalyst Tank Heater Circuit ? Voltage Below Normal, or Shorted to Low Source. Low signal voltage detected at the catalyst tank heater relay sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 1683 PID: SPN: 3449 FMI: 3 Catalyst Tank Heater Circuit ? Voltage Above Normal, or Shorted to High Source. High signal voltage detected at the catalyst tank heater relay sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 1682 PID: SPN: 3362 FMI: 11 Aftertreatment Diesel Exhaust Fluid Dosing Unit Input Lines – Condition Exists. An error has been detected by the catalyst dosing control unit.

Cummins ISB CM850 (2003-06) Fault Code: 1681 PID: SPN: 3361 FMI: 12 Catalyst Dosing Control Unit ? Bad Intelligent Device or Component. An internal error has been detected in the catalyst dosing control unit.

Cummins ISB CM850 (2003-06) Fault Code: 1679 PID: SPN: 3031 FMI: 2 Catalyst Tank Temperature ? Data Erratic, Intermittent, or Incorrect. The catalyst solution temperature sensor is not changing with engine operating conditions.

WARNING!