Exam 4: On-Board Diagnostic Scanners and Digital Storage Oscilloscopes

What selection tells the DSO when to begin displaying a waveform?

While discussing digital storage oscilloscopes: Technician A says the DSO shows the signals as they occur. Technician B says the DSO reads signals, stores them, and then displays them. Who is correct?

What type of data is stored while a DTC is being set?

The PCM monitors exhaust temperatures to detect cylinder misfires.

A technician is viewing a scan tool data stream to diagnose an OBD II system. The downstream HO2S has the same voltage switching rate as the upstream HO2S. Technician A says the air/fuel ratio is too rich. Technician B says the catalytic converter may be defective. Who is correct?

What are the advantages of the high-end OBD II scan tool compared to a code reader?

Technician A says all computer system problems can be solved by using a scan tester. Technician B says many computer-controlled components can be tested with an ohmmeter or voltmeter. Who is correct?

While discussing OBD II systems: Technician A says if a misfire condition threatens engine or catalyst damage, the PCM flashes the MIL. Technician B says the PCM illuminates the MIL if a defect causes emission levels to exceed 1.5 times the emission standards for that model year. 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?

While discussing scan testers: Technician A says scan testers 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 an OBD II emission control system, both pre-catalyst and post-catalyst oxygen sensors are used.

What type of signal is always on or off?

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?

The DSO sampling time is at least 20 times faster than other automotive testers.

What features are included in an enhanced OBD II diagnostic scan tool and what do they allow the technician access to?