Exam 4: On Board Diagnostic Scanners and Digital Storage Oscilloscopes

What are LTFT and STFT?

What type of signal is always on or off?

The CAN protocol will never be a required protocol for all manufactured vehicles.

What type of signal has a varying voltage within a specified range over a period of time?

While discussing scan tools: Technician A says scan tools have the capability to diagnose various computer systems on a vehicle. Technician B says scan testers have the capability to display data and DTCs and perform many other diagnostic functions. Who is correct?

On a DSO screen, what will happen if the time base selected is too long and the voltage range is set too high for the circuit being tested?

While discussing digital signals: Technician A says the leading edge of a digital signal represents a decreasing voltage. Technician B says duty cycle is the frequency at which a voltage signal occurs. Who is correct?

If everything in the system is functioning smoothly, both LTFT and STFT values should be close to 0.

How does the PCM determine catalyst efficiency?

Beginning in 1996, ODB II vehicles were equipped with a standard 18-pin DLC.

On an OBD II emission control system, are the oxygen sensors placed upstream or downstream from the catalyst?

Technician A says diagnostic scan tester operation varies depending on the make and model of the scan tool. Technician B says one of the major differences between OBD II and OBD I scan tools is how and where they are connected to the DLC. Who is correct?

While discussing the catalyst efficiency monitor: Technician A says if a fault occurs in the catalyst monitor system on three drive cycles, the MIL is illuminated. Technician B says if the catalytic converter is not reducing emissions properly, the voltage frequency increases on the upstream HO₂S. Who is correct?

On a DSO screen, what value is displayed horizontally?

While discussing LTFT and STFT when the STFT number is -20 and the LTFT number is -20: Technician A says these numbers indicate the PCM is trying to decrease fuel delivery. Technician B says these numbers indicate a normal condition. Who is correct?