What causes the U0100 code?

Dead ECU, severed CAN wiring; Faulty wiring harness connecting the respective sensor; Aging electrical connections or corrosion due to environmental elements specific to psa vehicles.

How to fix the U0100 code?

Conduct a complete OBD2 scan. Inspect the engine bay for loose connections related to Lost Communication With ECM/PCM A. Replace failed components with genuine OEM psa parts to ensure the fault does not return. Clear the ECU memory afterwards.

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PSA Group

🚨 Critical

U0100

PSA U0100 Lost Communication With ECM/PCM A

The U0100 diagnostic trouble code indicates an issue with the Lost Communication With ECM/PCM A. A notorious code on Peugeot/Citroen (PSA) vehicles, mainly resulting from dead ecu, severed can wiring. Found frequently across psa models utilizing 1.6 HDi, PureTech, THP engines, this code will illuminate the Check Engine Light and may cause the vehicle to enter Limp Mode to protect the mechanical components.

Brand

PSA Group

Fault Code

U0100

Severity

🚨 Critical

Models

Peugeot 207/208/3008/5008, Citroën C3/C4/C5, DS3/DS5

🛠️ Diagnostic Overview

Difficulty Level

🛠️🛠️🛠️ Hard (Advanced)

Estimated Time

⏱️ 3-6 Hours

🧰 Required Tools

✓ Digital Multimeter
✓ OBD2 Diagnostic Scanner
✓ Socket Wrench & Hand Tools
✓ Electrical Contact Cleaner Spray

⚠️ Possible Causes

• Dead ECU, severed CAN wiring
• Faulty wiring harness connecting the respective sensor
• Aging electrical connections or corrosion due to environmental elements specific to psa vehicles.

🔧 Recommended Fixes

→ Conduct a complete OBD2 scan. Inspect the engine bay for loose connections related to Lost Communication With ECM/PCM A. Replace failed components with genuine OEM psa parts to ensure the fault does not return. Clear the ECU memory afterwards.

🚨 This fault is CRITICAL! Stop driving immediately and consult a qualified technician.

🚗 Commonly Affected Vehicles