Cummins ISB4.5 CM2150 Fault Code: 343 PID: SID 254 SPN: 629 FMI: 12 Electronic Control Module Warning Internal Hardware Failure – Bad Intelligent Device or Component.

Posted by PerDiezel Solutions on January 21, 2026

Circuit Description
The electronic control module (ECM) receives constant voltage from the batteries through the unswitched battery wires that are connected directly to the positive (+) battery post. The ECM receives switched battery input through the vehicle keyswitch wire when the vehicle keyswitch is turned on.

Component Location
The ECM is connected to the battery by the OEM power harness through the ECM battery supply stub. This provides a constant power supply for the ECM. The location of the battery will vary with the OEM. Refer to the OEM troubleshooting and repair manual for component location.

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

Conditions for Setting the Fault Codes
This fault code is triggered when the internal ECM diagnostics detect a read or write error internal to the module.

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.

Conditions for Clearing the Fault Code
-To validate the repair, start the engine and let it idle for 1 minute.
-The ECM will turn off the amber CHECK ENGINE light immediately after the diagnostic runs and passes.
-The ECM will turn off the malfunction indicator lamp (MIL) after three consecutive ignition cycles that the diagnostic runs and passes.
-This fault code and malfunction indicator lamp (MIL) can also be cleared with INSITE™ electronic service tool.

Shop Talk
Make sure the ECM unswitched battery supply is coming directly from the battery and not the starter. If the unswitched power is coming from the starter, it is possible for the battery voltage to drop low enough during cranking to set this fault active.

This fault can also be caused by resistance in the ECM battery supply (+) or (-) circuits. Resistance in these circuits can cause the voltage level at the ECM input to drop low enough to set Fault Code 343 active.

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Cummins ISB4.5 CM2150 Fault Code: 338 PID: SID 87 SPN: 1267 FMI: 3 Idle Shutdown Vehicle Accessories Relay Driver Circuit – Voltage Above Normal, or Shorted to High Source.

Cummins ISB4.5 CM2150 Fault Code: 334 PID: 116 SPN: 110 FMI: 2 Engine Coolant Temperature – Data Erratic Intermittent or Incorrect.

Cummins ISB4.5 CM2150 Fault Code: 332 PID: SID 6 SPN: SID 6 FMI: 5 Injector Solenoid Driver Cylinder 4 Circuit – Current Below Normal or Open Circuit.

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Cummins ISB4.5 CM2150 Fault Code: 325 PID: 206 SPN: 656 FMI: 5 Injector Solenoid Driver Cylinder 6 Circuit – Current Below Normal or Open Circuit.

WARNING!