U0100 — Lost Communication With ECM/PCM "A"
Category: Network / Communication Severity: High
Updated:
DTC code U0100 means: Lost Communication With ECM/PCM "A". It falls under the "Network / Communication" category, with an estimated severity of High. Common causes include cAN bus wiring issue, faulty ECM/PCM and poor ground/connection; it's worth confirming the diagnosis before replacing parts.
Possible causes
- CAN bus wiring issue
- Faulty ECM/PCM
- Poor ground/connection
- Low battery voltage
- Software/configuration mismatch
Symptoms
- Several warning lights on at once
- Communication faults between modules
How to diagnose it step by step
- Measure battery voltage (weak cranking can set U0100).
- Check ECM fuses and grounds.
- Check the ECM connector.
- Measure the CAN bus (60 ohms).
- Replace or repair the ECM if it doesn't communicate.
How to fix it
Check the CAN wiring and grounds; it may be a control unit.
Estimated repair cost
From $0 (ground or battery) to $500–1,500 (ECU).
Frequently asked questions
What does DTC code U0100 mean?
Lost Communication With ECM/PCM "A".
Is code U0100 serious?
Severity High. Have it checked as soon as possible, especially if it affects safety or the catalytic converter.
Can I keep driving with code U0100?
Not recommended: the engine or transmission may fail without warning.
Related codes
U0101 U0121 U0140 U0151 U0155 U0164
Refine by car make
- Audi U0100: CAN wiring or ECM.
- BMW U0100: CAN bus or engine module.
- Ford U0100: CAN wiring or PCM.
- Opel U0100: CAN wiring or ECM.
- Peugeot U0100: CAN bus or engine control module.
- Renault U0100: CAN bus or engine control module.
- Toyota U0100: CAN bus or ECM.
- Volkswagen U0100: CAN wiring or ECM.
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