Indicates that some parameters readings of oxygen sensors are out of threshold. Could be due to the improper work of the catalytic converter, faults of oxygen sensors or other car systems. Could lead to the increasing of emission pollution and decreasing of engine efficiency.


  • Check Engine dashboard light is ON
  • Possible lack of power and car dynamic
  • Increased fuel consumption
  • Changed smell of exhaust gasses 
  • Could be issues with cold engine start


  • Faulty catalytic converter (due to resource or low quality fuel)
  • Faulty front or rear oxygen sensor
  • Leakage in exhaust system
  • Long term car running with unbalanced parameters (misfires, spark timing, high fuel pressure, oil leakage, etc.)

Severity - moderate

Does not have immediate danger effect to the car or driver. Indicates increased pollution and could lead secondary car systems malfunctions if not fixed in a reasonable time frame.


  • Be sure using a quality fuel. If not, change fuel, clear code and wait few days driving if it re-appears.
  • Check leaks in exhaust system: manifold, pipes, mufflers. Do fixes or replacement if required.
  • Check work of the front and rear oxygen sensors with working engine. It's expected that rear sensor have steady readings, the pulse rear readings indicates faulty converter.
  • Review and correct, if required, misfires, spark timing, high fuel pressure, oil leakage, injectors, engine coolant temperature sensors, other systems that have DTCs.
  • Inspect and replace, if required, oxygen sensor(s). 
  • Inspect and replace, if required, catalytic converter.