ASE Certification Practice Tests

6.

Answer A is wrong. Point A is the ground connection for the Engine Coolant Temperature Sensor, an (NTC) negative temperature coefficient sensor. The engine runs a startup strategy that enriches the air-fuel ratio when the engine's coolant is cold. These sensors have less resistance as temperature increases.

Answer B is wrong. The ECT sensor affects several different systems, like air conditioning and transmission. This signal affects EGR flow, enrich fuel mixtures, and delay torque converter, or A/C compressor engagement.

Answer C is wrong. The ECM uses different strategies programmed into its lookup tables for hot and cold operating conditions. This resistance results in delayed engine cooling fan engagement.

Answer D is correct. This is an EXCEPT-type question. The (ECT) engine coolant temperature sensor is a variable resistor that uses resistance to change a 5-volt reference signal from the ECM.

7.

Answer A is wrong. The (TPI) throttle position sensor is a potentiometer that indicates the throttle plate's angle to the PCM. The ECM uses this sensor's information along with several others to control injector pulse width and timing.

Answer B is wrong. The (IAT) or intake air temperature sensor is a thermistor that changes its signal according to intake air temperature. The PCM provides a richer air-fuel ratio as cool air passes the sensor. Cold air is denser and contains more oxygen than warm air does.

Answer C is correct. The exhaust gas recirculation valve regulates a small portion of exhaust into the combustion chamber. A stuck open EGR valve results in a rough idle. A stuck closed EGR valve results in high cylinder temperatures, NOx production, and engine knock.

Answer D is wrong. The (ECT) Engine Coolant Temperature Sensor continually sensing the temperature of the engine's coolant lowering its resistance as the engine warms to operating temperature.

8.

Answer A is wrong. The wastegates actuator and actuator diaphragm control a turbocharger's output. A stuck open wastegate results in underboost, poor engine performance, and a lack of horsepower.

Answer B is correct. The actuator opens the wastegate to divert exhaust away from the turbine, depriving it of its source of energy. A leaking or ruptured wastegate diaphragm doesn't divert enough exhaust resulting in an overboost condition.

Answer C is wrong. This compressed charge is denser in comparison to a conventional engine that relies on the downward stroke of the piston. The denser charge is forced into the cylinders by increased intake manifold pressure to provide additional engine horsepower.

Answer D is wrong. Most turbocharger failures are oil related. Contaminated and unchanged oil eventually results in bearing failure. Turbocharger seals are affected, resulting in oil consumption and blue-gray exhaust. Oil is mixing with the air-fuel charge and burning off in the cylinder.

9.

Answer A is wrong. A restricted fuel return line may result in a rich fuel condition. The fuel return line needs to flow freely for fuel to flow back into the tank.

Answer B is wrong. A ruptured fuel pressure regulator diaphragm results in high fuel pressure; remove the regulator's vacuum hose to see if there if there's fuel inside the hose.

Answer C is correct. A clogged or faulty fuel injector results in a misfire at that cylinder.

Answer D is wrong. Today's engines are port fuel injected, and the fuel injector's tips extend into the intake manifold just above the intake valve. A vacuum controlled fuel pressure regulator is used to compensate for the fluctuations in vacuum pressure.

10.

Answer A is wrong. High fuel pressure results in a rich fuel condition. The percentage will have a minus sign (-) preceding the number because the PCM is subtracting fuel; for example, -24%.

Answer B is correct. A vacuum leak results in excessive positive fuel trim. A positive number like (24%) indicates the PCM is adding fuel to compensate for a lean fuel condition. LTFT is a constant and stays in memory after the engine has been shut down. It's obtained from oxygen sensor input while the system is in closed loop.

Answer C is wrong. A ruptured fuel pressure regulator diapragm results in high fuel pressure, not a lean fuel ratio.

Answer D is wrong. A leaking or dripping fuel injector results in a rich air-fuel ratio. The PCM reduces the amount of fuel (negative - fuel trim) by decreasing the injector pulse width. This leaking injector would result in a negative LTFT.