What is the Exhaust and Emission System and what does it do?

fuel and emission systems

Your car or truck’s exhaust and emission system helps the engine run cleanly and efficiently, transforms  exhaust from your engine into gases that are safe to breathe, and transports them away from the vehicle.  Key components include the catalytic converter, oxygen sensors (O2 sensors), Power Control Module (PCM), Onboard Diagnostic system (OBD II), muffler, intake and exhaust manifolds or headers, and exhaust pipes.

Nitrous oxides and hydrocarbons from exhaust fumes are primary components of smog, and prolonged exposure to these toxins can cause asthma, cancer, lung and heart disease, as well as harming the environment.  Most vehicles made or sold in the U.S. are now built with internal combustion engines that run on unleaded gasoline or diesel fuel, and have highly effective exhaust and emission systems which greatly reduce these noxious pollutants.

The emission system, including the catalytic converter substantially reduces harmful gases, including carbon monoxide (CO), nitrogen oxides (NOx), and unburned hydrocarbons (HC).  Your exhaust system, including the muffler, also keeps the car quiet and helps your engine operate at optimum fuel efficiency.

Oxygen sensors (O2 sensors), mounted before and after the catalytic converter monitor and control the oxygen flow for optimum performance,  fuel efficiency, and pollution reduction. Older vehicles typically had two oxygen sensors to monitor and manage the air/fuel ratio, while newer models may require up to four O2 sensors.  Oxygen sensors are one of the most important and sensitive engine components, requiring tight calibration to OE standards.  Ignoring a bad O2 sensor can result in poor engine performance and cause damage to the catalytic converter.  Not only is their intended function critical, but if they malfunction by sending false trouble code readings, faulty O2 sensors can cause an expensive repair that may not have been necessary.

The Power Control Module (PCM) acts as the brain, or electronic control system for your vehicle. The Power-train Control Module (PCM) is often a combination of the Engine Control Unit (ECU) and the transmission control unit (TCU).  It reads the information provided by the O2 sensors and many other vital components, and directs the engine systems and components how to adjust operation for efficiency and safety.

The Onboard Diagnostics System (OBD II) provides self-diagnostic and reporting information on the vehicle, in the form of diagnostic trouble codes (DTC).  To read the DTC codes that have turned on the Check Engine Light, a scan tool, or code reader, is plugged into the 16-pin OBD II connector, usually located under the steering column.  These diagnostic codes provide quick and detailed information to help pinpoint engine problems and flag components and systems that need service or repair.

The emission system also reduces pollutants from gasoline vapors that can escape from the fuel tank. Your car’s exhaust system manages, transforms and transports gases from the engine out and away from the car and its occupants.

Symptoms your exhaust and emission system may need service or repair:

  • Check Engine Light illuminated
  • Loud noise from undercarriage or back of vehicle
  • Reduced power when accelerating
  • Rattling noise, that may be more noticeable when starting
  • Reduced fuel economy / poor gas mileage
  • Drowsiness while driving
  • Rotten eggs smell