• The Check Engine Light remains illuminated and multiple warning lights may appear at the same time.
• A scan tool reports U0100 Lost Communication With ECM.
• The scan tool cannot establish communication with the Engine Control Module.
• The 2017 MG ZS cranks but will not start.
• The vehicle starts intermittently and then suddenly refuses to start.
• Multiple control modules report communication faults.
• The ABS, ESC, or transmission systems may display additional communication-related fault codes.
• Warning lights return immediately after clearing fault codes.
• The instrument cluster may display abnormal warning messages.
• The engine may stall unexpectedly and fail to restart.
• Live data from the ECM is unavailable during diagnostics.
• Other modules remain accessible, but the ECM appears offline.
• The fault may occur intermittently after wet weather, battery replacement, or electrical repair work.
• Low system voltage may accompany the communication fault.

Possible Causes

The U0100 fault indicates that one or more modules on the vehicle network can no longer communicate with the Engine Control Module (ECM). The fault does not automatically mean the ECM itself has failed. On the 2017 MG ZS, common causes include low system voltage, battery or charging system faults, blown fuses, failed relays, poor ground connections, damaged wiring, corroded connectors, CAN network faults, or ECM power supply issues.

Because the MG ZS is a SAIC-developed vehicle, Chinese-market repair discussions frequently associate communication faults with connector issues, grounding problems, module power supply faults, CAN network disruptions, and occasionally Body Control Module or ECM communication failures. In New Zealand, coastal environments can also contribute to corrosion in connectors and grounding points, particularly on vehicles exposed to salty air.

Several different faults can produce the same U0100 code. Diagnostic testing is required before replacing any control module.

Is It Safe To Continue Driving?

Drive with Caution

If the vehicle is still running, communication with the ECM may be intermittent. The fault can worsen without warning and may eventually result in a no-start condition, unexpected stalling, or additional module communication failures.

Diagnosis

A U0100 fault cannot be accurately diagnosed from symptoms alone because the code may be caused by power supply faults, network communication faults, wiring issues, grounding problems, or a failed control module. Diagnosing the fault typically requires module network testing, CAN bus voltage checks, relay and fuse verification, connector inspection, and ECM power and ground circuit testing. The OEM Service and Repair Manual provides the factory communication network diagrams, ECM connector pinouts, CAN bus diagnostic procedures, wiring diagrams, connector views, module locations, grounding points, and fault-isolation flowcharts used by MG technicians to identify the root cause.

Recommended Resources

1. OEM Service and Repair Manual

Whether you are diagnosing an intermittent communication fault, tracing a CAN bus problem, or testing ECM power and ground circuits, this manual serves as the single source of truth you can rely on to eliminate guesswork, make the correct diagnosis, and complete the repair with confidence.

Click on the form below to order the OEM Service and Repair Manual that gives you direct access to the exact diagnostic and repair procedures used by MG dealerships.

2. Buy Replacement Parts

Need parts to complete the repair?

Click on the form below to order genuine or aftermarket parts that match your 2017 MG ZS and the repair being performed.