Practice question

A vehicle fails an emissions test for high CO (carbon monoxide). What does elevated CO indicate?

  1. Incomplete combustion due to a rich air-fuel mixture
  2. Excess air in the mixture causing a lean burn condition
  3. A faulty catalytic converter substrate
  4. A clogged diesel particulate filter

Answer: A — Incomplete combustion due to a rich air-fuel mixture

The correct answer is shown above. Try the full quiz for additional practice.

Practice more: Driver Fault Finding Test (DFFT) →