TorqueMech OBD Code Guide
U0100 - Lost Communication With ECM/PCM
A module lost communication with the ECM/PCM.
Code first. Confirm symptoms and checks before pricing parts.
Read code pattern
Check likely system
Estimate after confirmation
Common Next Steps
Turn the code into the next check.
Test charging voltage
Measure alternator output and battery voltage under load.
Inspect serpentine belt
Check belt condition, tensioner travel, and pulley alignment.
Verify battery condition
Charge and load test before blaming the alternator or starter.
Related Inspection
Code Overview
A module lost communication with the ECM/PCM.
Common Causes
- Low system voltage
- CAN wiring/connectors issue
- Module power/ground issue
- Module failure
Diagnostic Steps
- Check battery/charging system
- Scan for multiple U-codes
- Inspect CAN wiring/connectors
- Check module fuses/grounds
Related OBD Codes
Browse nearby codes when systems overlap.
Next Steps
Move from code to checks, then estimate.