Ecm codes: u0101, u0073 and u0100?

2014 CHEVROLET MALIBU
130,032 MILES • 2.0L • 4 CYL • 2WD • AUTOMATIC
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JAKNIYAH
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Recently got my engine harness wires fixed, made sure the gounding was in good condition. Car is giving out codes: u0101, u0073 and u0100. Is it possible for the ecm to be bad, and giving out them codes? And if the ecm is bad, where can I get a new one reprogrammed at?
Dec 18, 2025 at 1:28 PM
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JAKNIYAH
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also, will a no-good alternator have/send out the same codes: U0101, u0073 and u0100?
Dec 18, 2025 at 4:26 PM
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STRAILER
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If the battery is charged you should be okay for a short time but yes the alternator need to charge to keep the voltage above 12 volts.

U0073 - Control Module Communication Bus “A” Off
U0100 - Lost Communication With ECM/PCM
U0101 - Lost Communication With TCM

I would check all fuses with the key on using a test light

https://www.2carpros.com/articles/how-to-check-a-car-fuse

I would double check the wiring harness repair because these codes come up when the wiring is not correct. Please go over this guide and get back to us. Do you need the wiring diagrams and a guide on how to test the connections?
Dec 19, 2025 at 10:52 AM
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JAKNIYAH
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A guide on how to test the connections would be great.
Dec 19, 2025 at 11:46 AM
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STRAILER
  • ✓ASE Certified Mechanic
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Sure here is a guide on howe to test the connections.

https://www.2carpros.com/articles/how-to-check-wiring

Here is the wiring diagrams you need to help. You will need many so I would get the Alldata DIY sub for a couple of bucks for your car.

https://www.alldata.com/diy-us/en

Let us know how it goes.
Dec 20, 2025 at 11:34 AM
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