U0100 on Cadillac: How to Diagnose & Fix
Lost Communication with ECM/PCM
1 Cadillac model · 1 documented issue
U0100 on Cadillac by model: symptoms, diagnosis and fix
A low ELR 12-volt battery can leave control modules unable to wake and prevent a normal start. GM also issued VIN-gated program 14395A for a bounded 2015 OnStar-module battery-drain condition; that program expired in 2017 and is not proof of a universal drain.
Common Symptoms
- Control modules do not wake
- Vehicle will not enter Ready mode
- Low 12-volt battery after parking
How to Fix
Test the AGM battery and charging state, preserve DTC and low-voltage history, and diagnose the source of discharge before replacement. For a 2015 vehicle, ask a Cadillac dealer to check VIN and program history. This card does not cover a sudden loss of power while driving and does not prescribe a battery or maintainer.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Sources for this issue (2)
U0100 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does U0100 mean on a Cadillac?
U0100 stands for "Lost Communication with ECM/PCM." U0100 is a network communication code meaning a module has lost communication with the engine control module / powertrain control module (ECM/PCM) over the vehicle's data bus. The ECM/PCM is the brain that runs the engine, so when other modules can no longer 'talk' to it, the effects can be serious — a no-start, stalling, multiple warning lights, and many other modules logging faults at once. This is almost always a wiring, connector, power/ground, or bus fault, or a failure of the ECM/PCM itself, rather than a single sensor. It should be diagnosed promptly because the vehicle may be undrivable. On Cadillac it is documented across 1 model: ELR.
What are the most common causes of U0100?
The most common causes of U0100 are: Loss of power or ground to the ECM/PCM, CAN bus wiring damage, short, or open circuit, Corroded, loose, or damaged connectors at the module, Blown fuse feeding the ECM/PCM, Failed ECM/PCM, Another faulty module pulling down the data bus, Water intrusion or corrosion in a connector/harness. The specific cause varies by vehicle.
How much does it cost to fix U0100 on a Cadillac?
Repair costs vary widely with the root cause and Cadillac model; each issue on this page carries its own estimate where one is published.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.