Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC U0100: Lost Communication with ECM/PCM A: Action
CARRY OUT a self-test of the PCM. If the scan tool indicates that the module is not responding, REFER to COMMUNICATIONS NETWORK to diagnose the network communication concern. If PCM DTCs are present, REFER to the ENGINE CONTROLS - POWERTRAIN DTC CHARTS & DESCRIPTIONS (EXCEPT DIESEL & HYBRID) or for Hybrid, refer to ENGINE CONTROLS - POWERTRAIN DTC CHARTS AND DESCRIPTIONS (HYBRID) to diagnose the PCM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.