U0100 - Lost Communication With ECM/PCM A
U0100 is a generic network/communication diagnostic trouble code indicating Lost Communication With ECM/PCM A. It relates to the System-Specific system.
DTC Breakdown (SAE J2012)
| System | Network/Communication (U) |
| Type | Generic |
| Subsystem | System-Specific |
| Fault Index | 00 |
| Standard | SAE J2012 / ISO 15031-6 |
What does diagnostic code U0100 mean?
The vehicle logged U0100 after a communication failure occurred between modules on the CAN bus, specifically losing contact with the ECM/PCM control module.
Severity Level & Driveability Details
Severity: High
Loss of communication between safety-critical modules can shut down the engine, ABS, or power steering unexpectedly.
Common Symptoms of U0100
- Instrument cluster gauges dropping to zero or flashing.
- Multiple dashboard warning lights active (ABS, Airbag, Check Engine).
- Vehicle failing to crank or start.
- Loss of power steering or transmission control.
Typical Causes for U0100
- Low vehicle battery voltage or failed charging system.
- Open or short circuit in the CAN bus communication wires.
- Failed ECM/PCM control module assembly.
- Corroded or loose module connector plugs.
Diagnostic and Troubleshooting Steps
Test battery voltage and charging output to rule out power drops, and inspect primary grounding straps for the module.
Typical Repairs and Fixes
- Replacing a weak or failing vehicle battery.
- Repairing open or shorted CAN bus communication wires.
- Replacing or refitting corroded ground straps.
- Replacing or flashing the failed ECM/PCM module.
Sensor Location & Parts Involved
The CAN bus wires run throughout the vehicle wiring harness connecting the modules.
Clearing Code & Recurrence
Clear all module codes and perform a full system scan to verify that all modules are back online on the network.
Emissions & Smog Inspection Impact
The communication loss prevents the PCM from polling monitor status, making it impossible to pass inspections.
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Related Diagnostic Codes
Sources & References
This diagnostic guide is compiled and verified against the following authority sources:
- EPA OBD II Compliance Guidelines
- SAE CAN Bus Specifications
Frequently Asked Questions about U0100
What does the lost communication with ECM PCM module code U0100 mean?
The vehicle logged U0100 after a communication failure occurred between modules on the CAN bus, specifically losing contact with the ECM/PCM control module.
Is it safe to drive with the lost communication with ECM PCM module code U0100 active?
No, module drops can disable critical safety systems.
How much does it cost to repair a lost communication with ECM PCM module code U0100 fault?
Battery replacement is $150-$250, while wire repairs for the communication circuit run $150-$400 and module replacement with programming costs $600-$1,500.
What are the common causes of the lost communication with ECM PCM module code U0100?
Trigger conditions for the lost communication with ECM PCM module code U0100 include: Low vehicle battery voltage or failed charging system., Open or short circuit in the CAN bus communication wires., Failed ECM/PCM control module assembly..
Can I clear the check engine light for lost communication with ECM PCM module code U0100?
Clear all module codes and perform a full system scan to verify that all modules are back online on the network.
Will the lost communication with ECM PCM module code U0100 cause an inspection failure?
The communication loss prevents the PCM from polling monitor status, making it impossible to pass inspections.