U0100 on GMC
Lost Communication with ECM/PCM
U0100 on GMC vehicles indicates lost communication with ecm/pcm. Au7o has documented this code across 2 GMC models — most commonly on Hummer EV, Sierra 3500HD. 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. Typical repair costs on GMC range from $80 to $900, depending on the specific model and root cause.
Common Causes of U0100
- •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
U0100 on GMC by Model
GMC Hummer EV(1 issue)
- Multiple Warning Lights with Speed Limited to 36 MPH2022-2024
Owners report a cascade of warning messages appearing simultaneously — 'One Pedal Driving Unavailable,' 'Service ESC,' 'Service Trailer Brake System,' and 'Service Active Steering System' — with the vehicle's speed limited to approximately 36 mph. The issue appears related to communication faults between the vehicle's multiple electronic control modules, particularly affecting the electric stability control and four-wheel steering systems. The Hummer EV's CrabWalk and Extract Mode features may also become disabled. The issue can occur without warning and may require a dealer visit to clear.
GMC Sierra 3500HD(2 issues)
- Trailer brake controller / integrated trailer brake module malfunction2015-2023
Sierra 3500HD owners towing heavy loads report intermittent trailer brake output loss, warning messages, or erratic gain behavior from the integrated trailer brake controller. NHTSA complaints and GM service bulletins/diagnostics commonly point to module/software issues, poor connector pin fit/corrosion at the 7-way, or wiring faults that cause the system to disable trailer brakes unexpectedly.
- Electric power steering (EPS) assist loss / reduced assist warnings (new body style)2020-2024
On 2020+ Sierra 3500HD (T1 platform) with electric power steering, owners report intermittent loss of steering assist and warning messages such as "Steering Assist Reduced". NHTSA complaints and GM service information commonly point to EPS module/software issues, wiring/connector concerns, or rack-related faults that can occur without prior symptoms.
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View U0100 across all makes →Frequently Asked Questions
What does U0100 mean on GMC?▼
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 GMC specifically, this code is documented across 2 models.
What causes U0100 on GMC vehicles?▼
Common causes on GMC: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix U0100 on a GMC?▼
Repair costs on GMC range from $80 to $900, depending on the specific model and root cause.
Which GMC models have U0100 documented?▼
Au7o has documented U0100 on 2 GMC models: Hummer EV, Sierra 3500HD.