Cummins ISB CM850 (2003-06) Fault Code: 1698 PID: SPN: 3489 FMI: 4 Aftertreatment #1 Air Enable Actuator ? Voltage Below Normal, or Shorted to Low Source. Low signal voltage has been detected at the catalyst air solenoid circuit.

Posted by PerDiezel Solutions on January 18, 2026

This fault code is logged when the supply voltage to the air solenoid is less than +12 volts.

Possible causes:

1)Open circuit in the air solenoid signal wire
2)Open circuit in the air solenoid return wire
3)Shorted to pin to pin air solenoid signal wire
4)Failed air solenoid
5)Failed dosing control unit.

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 MIL lamp and fault code can also be cleared using the INSITE? 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 MIL lamp cannot be cleared using the INSITE? service tool.
4)The fault code will be cleared from memory after 400 days or 9600 hours of engine operation.

Possible repairs:

1)Replace the dosing control unit.
2)Repair or replace the OEM harness.
3)If necessary, calibrate the ECM.

Cummins ISB CM850 (2003-06) Fault Code: 1697 PID: SPN: 3489 FMI: 3 Aftertreatment #1 Air Enable Actuator ? Voltage Above Normal, or Shorted to High Source. High signal voltage has been detected at the catalyst air solenoid circuit.

Cummins ISB CM850 (2003-06) Fault Code: 1694 PID: SPN: 3234 FMI: 2 Aftertreatment Outlet NOx Sensor – Data Erratic, Intermittent, or Incorrect. An incorrect NOx sensor reading has been detected by the aftertreatment outlet NOx sensor.

Cummins ISB CM850 (2003-06) Fault Code: 1692 PID: SPN: 3234 FMI: 4 Aftertreatment NOx Sensor – Voltage Below Normal, or Shorted to Low Source. Out-of-range battery voltage has been detected by the aftertreatment outlet NOx sensor.

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.

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.

WARNING!