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.
U0100-00Lost Communication With ECM/PCMU0100-00LOST COMMUNICATION WITH ECM/PCMManufacturer communications
6Original wording in English
JEEP
Reported code forms U0100-00
Trailer Tow Module (TTM) Setting Active DTC U0100-00 – Lost Communication With ECM/PCM
JEEP
Reported code forms U0100-00
Transmission Wiring Harness Repair Or Replacement For No Start Or Stiff Steering This bulletin involves inspecting the transmission wire harness and installing mastic patch. If rub through is visible replace wire…
JEEP
Reported code forms U0100-00
"TRANSMISSION WIRING HARNESS REPAIR OR REPLACEMENT FOR NO START OR STIFF STEERING THIS BULLETIN INVOLVES INSPECTING THE TRANSMISSION WIRE HARNESS AND INSTALLING MASTIC PATCH. IF RUB THROUGH IS VISIBLE REPLACE WIRE…
DODGE, JEEP
Reported code forms U0100-00
Flash: Anti Lock Brake (ABS) Module System Enhancements This bulletin involves updating the Anit-Lock Brake System (ABS) module software. A small number of vehicles may have mismapped Diagnostic Trouble Codes (DTCs)…
DODGE, JEEP
Reported code forms U0100-00
Flash: Anti Lock Brake (ABS) Module System Enhancements This bulletin involves updating the Anit-Lock Brake System (ABS) module software. A small number of vehicles may have mismapped Diagnostic Trouble Codes (DTCs)…
JEEP
Reported code forms U0100-00
Harness Repair Or Replacement For No Start Or Stiff Steering This bulletin involves inspecting the wire harness and installing mastic patch. If rub through is visible replace wire harness. A small number of customers…
Check vehicle applicability
4A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
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.