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.
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.
Looking for U0100 on a different make?
View U0100 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.