What does this code mean?
A reporting module did not receive expected messages from the engine/powertrain controller. Record which modules report U0100 and which still communicate. Battery voltage, power supplies, grounds, connectors and network wiring should be tested before condemning a controller. The reporting module is not necessarily the failed module.
Sources and interpretation [1]
A code identifies a detected condition, not a part that must automatically be replaced.
Manufacturer wording
Source wording can vary by vehicle and suffix. It is shown as written, not as a universal diagnosis.
U0100Lost Communication With ECM/PCMU0100-00Lost Communication with Engine Control Module (ECM)Manufacturer communications
7Original wording in English
JEEP
Reported code forms U0100-00
Powertrain Control Module (PCM) Replacement Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation the technician may find one or more of the following Diagnostic Trouble…
JEEP
Reported code forms U0100
Flash: Powertrain Control Module (PCM) Updates Customers may experience the following: ? Engine Stop/Start does not work as expected and it is often automatically deactivated. Customers may also experience a Malfunction…
JEEP
Reported code forms U0100
Flash: Powertrain Control Module (PCM) Updates **Customers may experience the following: Stop/start function deactivated.**Customers may also experience a Malfunction Indicator Lamp (MIL) illumination. Upon further…
JEEP
Reported code forms U0100
Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further…
JEEP
Reported code forms U0100
Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further…
JEEP
Reported code forms U0100
Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further…
Check vehicle applicability
3A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
Historical vehicle association; OBD-II compatibility is not established by this record.
Historical records · 1 · Historical vehicle association; OBD-II compatibility is not established by this record.
Before replacing a part
Record codes and freeze-frame data. Check battery condition, related codes and visible wiring or hose damage. Follow the vehicle's diagnostic procedure and test results before replacing parts.
Sources and interpretation
These explanations are editorial summaries of the linked manufacturer material. PDF page numbers count from the first file page. Original publications are in English; translations are reference aids. A cited edition is not a claim that it is the manufacturer's latest instruction.
- Audi TT Quick Reference Specification Book · October 2013 ↗
Audi of America · PDF page(s) 143 ·
- 01-19-05TT / 2054867/7 · No start or ECM communication, U0100 ↗
Volkswagen Group of America · PDF page(s) 1, 2 ·
Source check date · 2026-10-27
Can I keep driving?
A code alone cannot establish whether driving is safe. A flashing malfunction light, severe shaking, overheating, oil-pressure warning or loss of braking or steering needs prompt attention. Stop in a safe place and seek assistance when control or engine safety is affected. Follow the vehicle handbook.