A previous blog entry about the Volkswagen emissions controversy tied in with some of the elements we teach in class, so I thought I’d provide a glance for automotive enthusiasts about some of our classroom activities.
Yesterday in our Fuel and Emissions class (AFD 231), instructor Adam Karch worked with students to understand how onboard emission monitors are actually completed on a running and driving vehicle. Students used a chassis dynamometer, an exhaust gas analyzer, and scan tool to monitor when and how the vehicle’s emission system checked each of the required emission monitoring systems.
The screen above shows the emission monitors that are being checked on a scan tool that is communicating with the vehicle’s onboard computer. The vehicle must be driven under different conditions that are programmed into the vehicle computer. The student has to drive the vehicle under different loaded conditions to get the vehicle’s onboard computer to check each of the required emission systems. The dynamometer displays a colored line on its display screen that is based on a program in the dynamometer that follows the proper drive cycle for emission testing.
The above image shows the line that must be followed on the dynamometer screen. The student increases or decreases vehicle speed and load to follow the requirements of the test. The drive cycle test is very specific in vehicle speed and load conditions. It often takes multiple attempts to drive a vehicle on public roads to get a vehicle to complete all the required tests. Slowing down to avoid traffic or obey posted speed limits will interrupt the test. It is much safer and easier to complete a drive cycle on the chassis dynamometer.
The chassis dynamometer also allows the instructor to be with the student in the learning environment to answer questions while the test is being competed. The student can then focus on learning and properly complete the test rather than traffic and general driving.
This learning activity also helps reinforce the importance of test-driving a customer’s car after a repair attempt has been made. If a technician determines an EGR valve has failed and replaces the valve, but does not test drive the vehicle under the correct conditions, the technician really does not know if the repair attempt has fixed the customer’s complaint. Driving the vehicle under the conditions that allow the onboard computer to complete a self-check is the only way to know definitively that the vehicle has been repaired.
This is only one example of many tests that your vehicle is continuously attempting to complete. Other tests might require the vehicle to sit unoperated for several hours or to be under a specific load and speed for several minutes.