Automotive Service Excellence: Advanced Engine Performance Practice Tests and PDFs

Both technicians are correct. A communication error between a scan tool and a vehicle can have many causes, such as a blown fuse, damaged data link connector terminals, an improper ground circuit of the data link connector, or a problem in the data bus network.

If the reading gradually drops by more than 3 in. Hg during the test, the exhaust system is restricted. The most likely cause of a restricted exhaust is a clogged catalytic converter, but a collapsed exhaust is also possible.

On the composite vehicle, the Engine Control Module (ECM), Transmission Control Module (TCM), and instrument cluster have software that supports functional testing. This can be done using a scan tool connected to the OBD port.

CAN High has a dormant voltage of 0.25 volts that increases to 0.65 volts when communicating. CAN Low has a dormant voltage of 11 volts that decreases to 4.65 volts when communicating.

A relative compression test uses a current probe and an oscilloscope to measure starter motor current. This information is used to determine the relative compression values of all cylinders. Then, the cylinder(s) with low compression can receive further diagnosis (e.g., a cylinder leakdown and/or compression test) to pinpoint the exact cause of low compression.

An injector balance test is used to find mechanical problems with fuel injectors. A lower than normal pressure drop reading indicates a clogged injector, while a higher than normal pressure drop reading indicates a leaking injector.

An open at ECM terminal 252 would prevent the crank sensor from working, resulting in a crank, no- start condition. A short to ground at terminal 204 would keep the cam position actuator on continuously, but would not cause a no-start condition. An open at ECM terminal 201 or a blown fuse #31 would result in a no-crank, no-start condition.

The air we breathe is made up of 78% nitrogen, 21% oxygen, and 1% other gases.

Both technicians are correct. The factory service information for a vehicle typically includes the spark plug gap, heat range, resistor requirements, part number, and torque. It also includes the spark plug wire resistance specifications.

Only technician B is correct. High oxygen (O2) readings upon start-up and at wide open throttle (open loop) are normal for a vehicle equipped with an electric secondary air injection pump since the pump is operated during these times.