U0100 · Generic

U0100 - Lost Communication With ECM/PCM

A module on the vehicle's communication network (commonly the body control module, instrument cluster, or transmission control module) has stopped receiving expected messages from the Engine Control Module / Powertrain Control Module. This is a network-level fault, not a specific sensor failure.

Full causes, diagnostic steps, and repair resources are available with a paid plan.

High severityModerate — some diagnostic tools helpful

Sourced from our reviewed reference database — not generated by DTC Technician.

Category (inferred from code structure)

Category: Network/Communication
Type: Generic OBD-II

Drive recommendation

A communication fault affecting the engine control module can appear alongside a stall or no-start condition. If the vehicle stalled or won't restart reliably, have it inspected before continuing to drive.

Most likely causes

MOST LIKELY

Blown fuse or open circuit powering the ECM/PCM

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Reported symptoms

Check engine light on, often with other unrelated warning lights
Multiple modules showing communication-fault codes at once
Instrument cluster gauges dropping to zero or acting erratically
No-start or stall, in more severe cases

Recommended diagnostic checks

Available with Pro Technician

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Frequently asked questions

Does U0100 mean the ECM/PCM itself is broken?

Not necessarily. It means another module stopped hearing from it — the actual cause is often wiring, a connector, a fuse, or low voltage rather than the module failing outright.

Technical details

Code: U0100
Make: Generic

This information is for diagnostic guidance only and is not a substitute for a qualified technician's in-person inspection. Always confirm a cause with the recommended tests before replacing parts.