MG ZS (Gen2) Catalytic Converter Fault

A Catalytic Converter Fault indicates that the Engine Control Module (ECM) has detected reduced efficiency or abnormal operation of the catalytic converter within the vehicle’s exhaust emissions control system. The catalytic converter converts harmful exhaust gases, including hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx), into less harmful emissions before they leave the exhaust system. The ECM continuously monitors catalytic converter performance by comparing the signals from the upstream and downstream oxygen sensors. When the converter can no longer effectively reduce emissions or becomes restricted, the ECM stores Diagnostic Trouble Codes (DTCs) and illuminates the Check Engine Light. A failing catalytic converter can significantly affect engine performance, fuel economy, and emissions compliance. This fault applies to the MG ZS Gen2 (ZS11 platform), introduced from 2024 onwards.

Symptoms

  • Check Engine Light illuminated
  • Reduced engine power
  • Poor acceleration
  • Engine hesitation
  • Increased fuel consumption
  • Rotten egg (sulfur) smell from the exhaust
  • Excessive exhaust heat
  • Rattling noise from the catalytic converter
  • Engine misfires (if caused by converter restriction)
  • Failed emissions inspection
  • Reduced fuel economy
  • Catalytic converter efficiency-related Diagnostic Trouble Codes (DTCs) stored

Possible Causes

  • Internal catalytic converter failure
  • Catalytic converter substrate melting or collapse
  • Catalytic converter blockage or restriction
  • Engine misfires damaging the catalytic converter
  • Rich air-fuel mixture causing catalyst overheating
  • Oil contamination from excessive engine oil consumption
  • Coolant contamination due to internal engine failure
  • Faulty upstream or downstream oxygen sensor
  • Exhaust leak affecting oxygen sensor readings
  • Incorrect fuel trim caused by engine management faults
  • Physical impact damage to the catalytic converter
  • Faulty Engine Control Module (ECM) (rare)

Diagnosis

Diagnosis begins by confirming any stored Diagnostic Trouble Codes (DTCs) and reviewing freeze-frame and live data using a compatible diagnostic scan tool. Live data should be monitored for upstream and downstream oxygen sensor activity, fuel trim values, air-fuel ratio, engine load, and catalytic converter efficiency. The technician should inspect the exhaust system for leaks, damage, loose heat shields, or signs of impact to the catalytic converter. The oxygen sensors should be tested to verify correct switching operation and heater circuit performance before condemning the catalytic converter. Exhaust backpressure testing or intake manifold vacuum testing should be performed to determine whether the catalytic converter has become internally restricted. Temperature measurements before and after the catalytic converter may also be used to assess catalyst efficiency. The technician should inspect for engine misfires, excessive oil consumption, coolant leaks, injector faults, or ignition problems that may have caused catalytic converter damage. Manufacturer diagnostic procedures may also include oscilloscope waveform analysis, emissions testing, catalyst efficiency monitoring, ECM input verification, and software updates where applicable.

For vehicles operating in New Zealand, following OEM diagnostic procedures helps accurately distinguish between a failed catalytic converter, oxygen sensor fault, exhaust leak, engine misfire, fuel system problem, ignition fault, or engine mechanical issue before replacing expensive emissions control components.

Accurately diagnosing this fault often requires manufacturer testing procedures, wiring diagrams, exhaust system schematics, oxygen sensor specifications, catalyst efficiency test procedures, exhaust backpressure specifications, fuel trim reference values, oscilloscope waveform examples, emissions control diagnostics, ECM control strategies, live data reference values, and system calibration information. Access to the factory service manual significantly reduces diagnostic time and helps prevent unnecessary parts replacement.

Applicable Years

2024, 2025, 2026, onwards

To order the correct OEM Service and Repair Manual for your MG ZS, submit your request using the form below, and our team will provide the ordering details.