MotorBitU0100: Lost Communication With ECM/PCM A
Another module cannot talk to the engine computer on the CAN bus. This is a network code, not a spark plug code.
Educational OBD2 information. Confirm on your vehicle with a scan tool. MotorBit can read this code, freeze frame, and live data over an ELM327 adapter.
What U0100 means
U0100 is a communication timeout with the PCM.
Why the check engine light comes on
Multiple warning lights can appear because modules share data. The check engine light is often one of them.
Common causes
- Low battery voltage
- Aftermarket stereo/alarm wiring
- Failed PCM
- Damaged CAN wires
- Bad ground
Typical symptoms
- No-start
- Cluster warnings
- Scan tool may not connect
What to do next
- Charge/test the battery first.
- Check grounds and recent electrical work.
- If the car runs, still inspect CAN wiring — intermittent U-codes are often voltage related.
How MotorBit helps
Open MotorBit, connect your ELM327, and read U0100 with freeze frame (RPM, load, temperature, speed at the moment the fault set). Then watch live PIDs and fuel trims instead of replacing parts by guesswork. When the repair is verified, clear the code and re-check monitors.
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FAQ
Is U0100 serious?
Severity is listed as high on this page. Misfire, crank/cam, and communication codes deserve faster attention than a tiny EVAP leak.
Will disconnecting the battery clear U0100?
It may hide the lamp temporarily, but the fault usually returns and you lose freeze-frame evidence. Scan first, then clear after the repair.
Can MotorBit clear U0100?
Yes, after you understand the cause. Clearing without a repair is how the light comes back on the next drive cycle.