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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  • 31 POSTS
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 5:28 AM

What to check next

Diagnostic guidance. Suggested checks and possible repairs are separate from the owner's reported results.

Obtain a complete scan and have the harness repairs checked against the wiring diagram, including affected connectors and module supplies. Test the battery and charging system rather than inferring their condition from the communication codes.

Guidance references and applicability

2CarPros: Original discussion 1711655 https://2carpros.com/questions/ecm-29600924 Source for reported history and outcome. Contributor suggestions are not independently confirmed diagnoses. Attachments were not verified. Fluke: Diagnosing voltage drops https://www.fluke.com/en/learn/blog/automotive/electrical-automotive-troubleshooting General support for checking supplies and grounds under load. Follow the matching wiring diagram and test limits; this does not identify a failed component.

Read the replies · Discussion summary and reported outcome

AI-ASSISTED GUIDANCE · REVIEWED BY 2CARPROS
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JAKNIYAH
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  • 31 POSTS
also, will a no-good alternator have/send out the same codes: U0101, u0073 and u0100?
Dec 18, 2025 at 8:26 AM
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STRAILER
  • ✓Experienced Mechanic
  • 55,540 POSTS
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 2:52 AM
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JAKNIYAH
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  • 31 POSTS
A guide on how to test the connections would be great.
Dec 19, 2025 at 3:46 AM
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STRAILER
  • ✓Experienced Mechanic
  • 55,540 POSTS
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 3:34 AM
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Discussion summary

Ecm codes: u0101, u0073 and u0100?

After engine-harness repairs, the owner reported U0101, U0073 and U0100 and asked whether the ECM or alternator could be responsible. The discussion recommended checking the repaired wiring, electrical supplies and connections.

Reported outcome: No failed module, charging-system fault or successful repair was reported.

The actual repair locations, voltage measurements and network test results were not supplied. The codes alone do not establish an ECM replacement requirement.

Read the original discussion

AI-ASSISTED SUMMARY · REVIEWED BY 2CARPROS
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