Fault Code 1688
Cummins
Engine Control Module Internal Error
Controller displays Fault Code 1688 – ECM Internal Failure
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Internal ECM hardware fault, Corrupted ECM software, Severe voltage spike or grounding issue
How to Fix / Troubleshooting
Safety first: Disable automatic start. Do not repeatedly attempt to start if ECM fault persists.
- Power cycle: Turn off DC power to the ECM (if possible) for several minutes, then restore and see if the fault clears.
- Check power and grounds: Verify ECM supply voltage and ground integrity. Poor grounding can mimic ECM faults.
- Inspect harness: Look for shorts or damage that could have caused an overvoltage condition.
- Professional service: ECM internal faults typically require Cummins diagnostic tools for reprogramming or replacement. Contact an authorized service provider.
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Repair Difficulty
Professional Required
5/5
Required Part
Engine Control Module (ECM)
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