HC | CO | NOx | Possible Cause or Recommended Action |
High | High | High | Replace converter and O2 sensor;verify tune-up and correct any faults |
High | Low | High | Replace converter; tune-up & check lean; AFR; leaking exhaust valves. |
Low | High | High | Replace converter and O2 sensor. |
High | High | Low | Rich AFR; air injection. |
High | Low | Low | Run-in converter; tune-up; oil change. |
Low | Low | High | EGR; lean AFR; leaks; run-in converter; use larger converter; |
Low | High | Low | O2 sensor; rich AFR. |
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