Exam 9: Strategies of on Board Diagnostic Continuous Monitors

Technician A says the functional test observes the reaction of an output device to a command from the PCM. Technician B says with a scan tool you can access the Readiness Status menu to determine which monitors have run. Who is correct?

What type of tests does the comprehensive component monitor perform, and when does the it run?

Explain what a Type A misfire is and how the PCM reacts to it.

What type of logic does the comprehensive component monitor use when determining whether or not to set a DTC and illuminate the MIL?

When does the fuel system monitor run, and what is its role?

Technician A says the learned LTFT corrections are used as a new base line for STFT. Technician B says the STFT values are constantly adjusted by the PCM to correct for rich/lean running conditions. Who is correct?

Technician A says the comprehensive component monitor continues to run until all sensors have been tested once. Technician B says the rationality test checks to see if the input values from a sensor make sense, based on the current operating conditions at the time the test is performed. Who is correct?

How does the PCM detect a cylinder misfire?

What are the basic causes of a cylinder misfire, and what adverse effect do they have on tailpipe emissions?

A Type A misfire is a misfire that will cause emission levels to exceed 1.5 times the FTP and will set a code but will not turn on and flash the MIL until the second consecutive trip where it is detected.

What causes a misfire to occur?

Which of the OBD II monitors checks circuit integrity?

The comprehensive component monitor will use one-trip or two-trip logic when determining when to set a DTC and illuminate the MIL.

When does the comprehensive component monitor run?

Technician A says the comprehensive component monitor keeps track of outputs that could affect vehicle emissions. Technician B says the comprehensive component monitor performs rationality testing of the MAF sensor. Who is correct?

How does the PCM use short-term fuel trim (STFT) information?

Technician A says the comprehensive component monitor will use three-trip logic when determining when to set a DTC and illuminate the MIL. Technician B says an OBD II system requires a drive cycle to occur that meets specific enable criteria before the monitors will run to completion. Who is correct?

What is long-term fuel trim (LTFT)?

A misfire occurs when the air/fuel mixture in the combustion chamber ignites and complete combustion occurs.

The continuous monitors act as a safety gate against emission system failure that could result in increased pollutants being emitted.