Exam 34: Emission Control Diagnosis and Service

A vehicle is in the shop because it failed an emissions test due to excessive carbon monoxide [CO]. The fault was a bad oxygen sensor that was easily replaced. Technician A says that the EGR system should be checked before the vehicle is retested. Technician B says the vehicle should be tested with a five-gas analyzer before it is retested. Who is correct?

A scan tool can be used to diagnose a faulty ______.

Which of the following emission systems is typically NOT controlled by the PCM?

To monitor the vapor purge in most systems, the PCM changes the duty cycle of the purge solenoid while monitoring the ______.

In an engine in good condition running at 2,000 rpm, with a working EGR system, NO_X should be below _____ ppm.

A dirty air filter may cause lower than normal ___________________ emissions.

Spark knock may be referred to as ____________________.

Technician A says a defective PCV valve may cause rough idle operation. Technician B says the PCV system depends upon a properly sealed engine to perform correctly. Who is correct?

A rich air fuel mixture will cause high ____________________ emissions.

Technician A says if the EVAP system is purging vapors from the charcoal canister while the engine is idling, rough engine operation will occur. Technician B says the system should not have more than 0.5 liter of flow during the 240 seconds of an I/M 240 test. Who is correct?

An excessively lean air/fuel ratio resulting in misfires causes HC emissions to ____________________.

An AIR system should be checked for overall efficiency by looking at the changes in exhaust quality when the system is turned on and off.

A restricted or plugged ___________________ system may cause excessive HC and CO emissions.

Technician A says a defective throttle position (TP) sensor will not affect the EGR valve operation. Technician B says a defective engine coolant temperature (ECT) sensor will not affect the EGR valve operation. Who is correct?

Technician A says CO emissions increase as the air/fuel ratio becomes richer. Technician B says CO emissions increase as the air/fuel ratio becomes leaner. Who is correct?

Excessively high ____________________ emissions can be caused by any condition that prevents the EGR from allowing the correct amount of exhaust gases to enter the cylinders.

The customer complains of a loss of power at highway speeds and a rough running engine at all speeds. A five-gas analyzer reveals these measurements at 2,500 rpm: HC = 700 ppm, CO = 0.2%, CO₂ = 9.2%, O₂ = 6.2%, and NO_X = 330 ppm. What is the most likely cause?

Low CO indicates a lean mixture; as the mixture becomes more lean, HC increases.

Before the EVAP system on an OBD-II vehicle can be pressure tested or smoke tested for leaks, a scan tool must be used to _____.

An exhaust ___________________ is one of the valuable diagnostic tools for driveability problems.